I remember in the original AD&D books there was something on the prices of building a castle. Cost for a tower, a length of wall, a drawbridge etc. Does anyone recall this, or know where I can find it (or a better version)? I want to bring in castle building for my team of players.
There was a 3.0 version, the Stronghold Builder's Guide, that is probably more relevant to 3.5. Given the nature of the material, I don't think it would require much of an update. (Unless the wealth guidelines changed dramatically between editions?)
The AD&D book you're remembering is 2nd edition's Castle Guide. I think I actually have a copy of that stashed somewhere in my parent's place, though I haven't seen it in years. :)
Some of the reviews on Amazon indicate that it used to be available for free from TSR's homepage. (One of the reviews is from 1997!) I doubt WotC has it up, though.
There were also prices and DMing guidelines for castle-building by players in the 1st edition DMG, pp. 106–108.
For a more old-school approach, you might try the Adventurer Conqueror King System (ACKS). One of the primary goals of the system is to make good on D&D's promise of barony-building and rulership for powerful PCs.
All classes gain access to strongholds, usually at level 9. Those strongholds have different costs and functions within the game world, with a reasonable explanation attached too. For instance: why do the strongholds of powerful mages include monster-filled dungeons? Because those mages build tunnel complexes to attract monsters in need of lairs. Why? Because the mages need those monsters for exotic organs and other magical ingredients and reagents.
ACKS is a strong OSR game with a rational and self-consistent set of rules and assumptions. It also has what looks like the bones of a workable economy.
EDIT: In response to SevenSidedDie's comment about no per-piece pricing:
There is a table of costs for constructing strongholds (pp. 126-127) that has a good selection of:
- various types of doors
- various types of stairs
- structural elements
Pathfinder Adventure Path #32: Rivers Run Red (Kingmaker 2 of 6) is largely compatible with 3.5 and contains:
Expansive new rules for running your own cities and nations, by James Jacobs.
These are going to be expanded upon in Ultimate Campaign, a recently announced 2013 source book which will contain rules for:
building strongholds, attracting followers, and conquering kingdoms through warfare or guile…
The DMG v3.5 (p.101, table 3-27) lists costs of a few buildings.
For example: Castle for 500,000gp; Huge castle for 1,000,000gp; Moat with bridge for 50,000gp; etc.
From there, you should be able to figure a decent approximation for whatever specifics you have in mind.
Late edit: this answer correctly points out that the crafters can actually pay 1/3 of the final price.