also, since the title is "building a 29er", regarding build vs buy:

if you're buying all-new you can almost never beat the package price of a new complete bike that is on sale. you can sometimes beat MSRP, especially if you're willing to go grey market on ebay. (buying stuff from china and taiwan that bypasses US distribution and possibly even the manufacturer.)

where building really pays off is if you have some existing stuff you're going to re-use, or if you're buying a major item used. if you buy a used frame and fork, you've potentially saved a boatload of money. it's the same type of savings as buying a complete used bike.