Now we all know that GMs don't like letting players have undead. As a necromancer enthusiast i have had to deal with half compromises and patronizing "oh, no, i'm not running an evil campaign, take something else" or "well, alright, you'll be burning your 3rd level spell slot all game... But you can do that if that's what you want. You only get 2 though." And that's just not good enough, ladies and gentleman. It's not even close to good enough. If a player wants to command an army of undead it's an entire adventure in itself! And it opens new interesting tactics for you GMs! You could have a necromancer have an entire RTS mechanic as his allies clash with another army: while the fighter, cleric and rogue push forward into the opposing army, the wizard on his undead wyvern mount directs the un-breathing army, holding the line and directing detachments to flank, the other army loosing a cavalry against the flankers, measure and countermeasure raising the stakes!
Anyway, my plea for your consideration over, these spells are suitable for D&D 5e, pathfinder 1e, or D&D 3.5:

Create undead (rework):

Necromancy 1 Sor/Wiz/Cleric
Components: Vocal, Somatic, Material
Casting time: 1 round [60 seconds]
Material costs: a pinch [1 oz] of bone powder, pinch of grave soil, a drop of blood, a dead body(s) appropriate for the undead you're attempting to raise
The created undead are under your control until their destruction, dismissal, or until you exceed the number of undead you can control. They follow your commands to the best of their abilities and may be instructed to follow, guard an area, destroy a target, or move an object. You may control a number of undead equal to your spellcasting ability modifier multiplied by your caster level, until you reach 20th level when you may control any number of undead outside of direct combat. If you create more undead than you can control, the GM decides which of your horde are released from your control, unless you attempt to specifically release a specific undead (arcana check DC= the released creature's CR + 10). You may control up to 4 undead in direct combat, with this limit also counting towards constructs, undead or summoned NPC allies conjured or created by other spells or abilities. If a player commands more than 2 undead they control in direct combat, they cannot cast a spell that turn.The following levels describe how many undead of a given type you may raise with a single spell slot of the given type

Level 1 - up to 4 evil eyes (custom monster), crawling hands, skeletons and/or zombies
Level 3 - up to 2 ghouls and/or ghasts, or up to 6 skeletons, zombies and/or evil eyes
Level 4 - up to 2 mummies or mohrgs, up to 4 ghouls or ghasts, or up to 8 skeletons/zombies
Level 5 - 2 mummy lords, 4 mummies or mohrgs, up to 4 ghouls or ghasts, or up to 8 skeletons/zombies
Level 6 - 2 shadows/wraiths, 2 mummy lords, 2 wights, 4 mummies or mohrgs, 8 ghouls or ghasts, 10 skeletons or zombies
Level 8 - a devourer, 2 spectres, 4 shadows/wraiths, 4 mummy lords, 8 mummies/mohrgs, or up to 4 graveknights.
Level 9 - add 2 to the highest total of a given undead type mentioned above and raise that many; these undead gain a number of HD equal to your spellcasting ability modifier.

Create skaab
3rd level necromancy (wizard, cleric)
Somatic, material components: 2 or more dead bodies sewn together, necrogen (a mixture of effluvia [liquid corpse juice], lead powder and bog water or water that contained rotting biomatter)
@10th caster level created skaabs gain an additional 2 HD and +4 to ONE bas stat (upping the respective limits)
@15th caster level the created skaab gains 4HD and +8 to distribute among the base scores
@20th caster level the created skaab gains 6 HD and +10 among attributes, and the player may control as many skaabs OUT OF COMBAT as they wish, in direct combat still only 4 can be managed without feats.

A skaab is a composite undead stitched together from disparate parts and is animated by necromancy and the vile substance called necrogen, which replaces half the masse's original blood. Skaabs come in innumerable forms, limited only by the deranged imaginations that bind them together (and the laws of physics and anatomy). A skaab's stats, attacks, senses, move speed and CR are determined by it's components and grafted weapons. They possess no true intelligence (usually) but understand how to use weapons or grafted parts. Each part carries with it a statistic from it's original owner;
The torso defines the base CON and Hit Dice. Adding more torsos grant their CON bonuses to the base CON and their HD to the HD pool. Thus it's important to make the base torso that of a hardy creature. Additional torsos can be added so long as their bonuses do not exceed more than half the base torso's CON score, or they become limp and useless, adding nothing. If the base torso has natural armor bonuses or natural armor, you may add those, but adding manufactured armor will overrule any natural armor.
Heads determine the senses, intelligence, and number of attacks available to the skaab. The main head is the one connected to the primary torso or torso bundle where a head would attach naturally, and determines the base INT score. The base head adds all the attacks and senses it had in life, and each additional head adds 1 attack and 1 sense it possessed in life, as well any natural bite attacks it had in life. A skaab cannot have more heads than half the base head's INT, and cannot have more than 6 attacks. This Int limit may be tracked seperately for hydra heads, but still cannot give a skaab more than 6 attacks.

Arms determine the base strength and kinds of attacks available to the skaab, such as held weapons, claws, tentacles, etc. One pair is designated by the caster as the base pair of arms and that pair determines the base STR score, and each additional set adds their strength modifier to the base score, up to a max STR of 24. Past that, additional limbs just add attack types available or arms available to manipulate or hold objects. Forelimbs from quadrapedal creatures may be used as arms but cannot hold weapons if they dont possess hands or tentacles or have such appendages added to them, or have weapons grafted directly over their end.
*A note: arms add forms of attacks, not additional attacks. If an arm or pair of arms wield a weapon, they can use that weapon to attack, but may not attack more times than the number of attacks allotted by the skaab's heads.

Legs determine the base DEX score and land move speed. As with arms the skaab's creator determines a base pair of legs that contribute the base DEX and move speed, with additional sets adding their DEX bonuses to that score and half their original move speeds to the total, not exceeding the base DEX+1/2 base DEX. However, legs must be spaced so as not to interfere with each other's movement, and must be appropriately sized to move the skaab. A giant torso cannot move with a single pair of normal person's legs, but could move with 11 pairs of such legs arranged along it's underside like a centipede's, though sturdier legs would be better suited to the job and such an arrangement would reduce the whole creature's move speed.

Other: Tails, wings, fins, flukes, flippers, tentacles, eye stalks, weapons and armor grafted to the frame of the skaab all add their logical bonuses or attack types. Most of these are move speeds, but some may add extra senses are new attack options like projectiles or beams/rays. This could also be mouths and eyes added on. A weapon grafted to a limb adds that weapon's attack type to the skaab's available repertoire of attacks.

The logic of a skaab: while the above describes the basic mechanical rules, create skaab relies partially on role play logic and the reality of anatomy. A ghoul stitcher (person who creates skaabs) can't just attach a limb willy-nilly and expect it to function. Each limb needs proper anchoring, musculature, ligaments and integration into the whole. The necrogen does much of the fine work of connecting nerves, tendon, muscle and veins/arteries, but bone work must be done to give limbs base joints. The work involved in creating a skaab worthy of the name can take days. When cast above 3rd level extra limbs will form rudimentary, cancerous looking joints and connections that are weaker than natural or "sculpted" work. Cast At 6th level, so long as dead bone, flesh, tendon and organ material that's been doused with necrogen is present, the skaab will automatically consume it to form "natural" joints and connections. Ideally, anything more complex than a zombie with 6 arms, 6 legs, and 3 heads should be drawn out to show how the character assembles the creature. If it looks like a disjointed mess on paper, it probably wont function in play. A simple diagram is all that's necesarry, a player or GM need not have an art degree, just a sketch that gets the basic concept and execution across.

A variant of this allows the limbs to simply create their own joints, but it's still suggested that the player still draw what they intend the thing to look like.

A player may only control a number of skaabs equal to their spellcasting mod multiplied by their proficiency, and may control no more than 4 in direct combat. At level 20 the player may control as many skaabs outside of combat as they want. The in-combat limit also counts any other undead, constructs, conjured creatures or summoned allies under the player's control. If a player commands more than 2 skaabs they control in direct combat, they cannot cast a spell that that turn.