Starting a Settlement

[Azreal]

Are there any established rules or homebrews for starting a settlement and looking at costs, time, population and such for 5e?

The hook I want for this sandbox campaign is my PCs would be starting up a settlement in an extremely deadly world where the majority of people live behind walled city-states similar to Attack on Titan.

[Estrillian]

There are building cost guidelines in the DMG, as well as costs for skilled and unskilled hirelings. A reasonable approach would be to make a guesstimate for how many workers you need for the fields / farming to feed your builders and assume that it costs you the same as hiring them.

A more realistic approach probably starts a settlement with a group of people who can both build their own houses and produce their own food, without cost to the PCs, so long as they are provided with suitable protection. i.e. if the PCs fight off monster X and deal with natural threat Y then the settlers can build their own settlement, complete with basic defences (a ditch, a dirt bank, a palisade). Once built it is handled like a PC owned business (the rules for those are in the lifestyle section of the PHB), self-sustaining as long as it receives appropriate minimal PC attention, but generating little in the way of excess wealth.

Once you have a basic settlement you need to look at the advanced stuff, the fortifications, public works and the like. A basic settlement won't produce much in the way of excess food/supplies, and what it does would probably be better stored against disaster. Similarly it probably won't have much in the way of excess workforce, since agriculture/hunting will take most of their time. You either have to accept that any building project will be vanishingly slow (i.e. the farmers only work 50-60 days a year on it, and completion takes decades) or provide some extra input to the process, usually by hiring in workers from somewhere else.

The DMG gives some sample costs and building times for different construction projects, with costs in Gold. Most likely the actual cost is split up between cash pay, food, and living expenses. Depending on the sophistication of your world's economy the main cost is probably food, rather than coin. For example the Pyramid Builders were paid in bread, grain, beer, etc. and given homes provided by the ruler to live in while they built. Actual coin was probably not involved. Since your starting settlement isn't producing excess food in the first place you probably need to buy in food from somewhere else. If you can do that then the DMG rates probably work well enough. If you can't then the big challenge for the PCs is to work out how to support the workforce they need (create food and water? killing and eating gigantic beasts? working slaves to death on starvation rations?) for the job. I'd also note that the DMG building rates are only suitable for a well-established sort of late medieval building rate. If your game is set further back in history then really big projects probably take lifetimes to build. If it is more recent then times go down.

If you aren't starting from scratch, i.e. your settlement is already established, then you can try and do things with taxation. I ran a game once a lot like this, where the PCs inherited a half-ruined town and wanted to rebuild it. They could set the tax rate, but ran the risk of rebellion if they kept it too high. This works best if your settlement has some trade to profit from. If it is on a trade route (a road or a river) or produces some sort of commodity (such as a mine) then you can assume a much higher level of excess wealth, which you can then tax to pay for your hired workers.

[Gastronomie]

Depends on how much casters there are in the world.

For instance, in a world where mid-level casters are common, Wall of Stone and stuff like that can help construct buildings with wonderful speed. And stuff like that.

[Azreal]

In this world a lot of arcane knowledge had been lost and the Gods quiet. The world itself is high magic with low magic Races.

[Estrillian]

In this world a lot of arcane knowledge had been lost and the Gods quiet. The world itself is high magic with low magic Races.

I almost assumed that the DMG rules assumed that PCs were using magic to help, since construction goes far slower when they are not around.

[JackPhoenix]

I almost assumed that the DMG rules assumed that PCs were using magic to help, since construction goes far slower when they are not around.

I don't know, it fits my experience with RL constuction workers without supervisor present.

[indemnity]

Are there any established rules or homebrews for starting a settlement and looking at costs, time, population and such for 5e?

I played a campaign that used Pathfinder Kingmaker rules but changed into 4e. We played in a living world and it the rules even encouraged play outside the game day.

It used the Kingmaker Adventure Path (book 2, chapter 2) (http://paizo.com/pathfinder/adventurePath/kingmaker) and Ultimate Campaign (http://paizo.com/products/btpy8vdl) changes. Free examples can be found at d20pfsrd (http://www.d20pfsrd.com/gamemastering/other-rules/kingdom-building).

The rules almost make a mini Civ-type game with a world map, town map, functional roles and a new currency.

Generally, the balance of costs/times/population are directly covered. Plus plenty of user-created online tools, calculators, maps, etc.