Creating odd gear

[Vendarien]

Ok the character I always like to use is a Dwarven cleric of the scholar god Dugmaren Brightmantle. Well in some of the books it says this
"Members of Dugmaren's clergy dress
practically when exploring dangerous or unknown territories.
Most favor light armor and weapons, preferring maneuverability
over defense. Many carry unique weapons; most also have
items with defensive capabilities of widely varying usefulness
and reliability, which they have invented and wish to field-test."

and it has got me thinking. Are there any rules in D&D for self engineered equipment or items or how you would go about creating new things like that or is it all DM rule and made up as you go? I like to use very out of the box techniques and would love to be able to invent some weird ify gear to go with it.

[BowStreetRunner]

Well, obviously there are sections in the DMG and MIC that cover creating custom magic items, and DMG2 p 229 has a section on Signature Traits for magic items. But if you are referring to custom non-magic items I have never seen anything official. Unofficial, yes (http://www.giantitp.com/forums/showthread.php?t=158057). But not official.

[Slipperychicken]

You could take the magic item price guidelines and apply it to nonmagical enhancements. Include some clause like "you need a plausible explanation approved by the DM for how a nonmagical item would produce such an effect", as well as requiring things like tune-ups and fuel. "Fuel" would include ammunition, oil, coal, repairs, maintenance, etc. All of this would be abstracted as gp cost in materials per X uses, and time/equipment to maintain the equipment before it becomes nonfunctional.

Dungeonscape has some nonmagical weapon enhancements and miscellaneous equipment, Complete Adventurer, Complete Scoundrel also have some interesting gear pre-written.

BoVD has rules for trapping items and equipment (much the same as regular trap rules). Basically you pay for the cost, and just apply the trap to anyone who wears it. Not much of a stretch to say you can have the "traps" oriented outward and be controlled by the user.