[onewhippedpuppy]

Without serious collateral you are a risky proposition. At least most contractors have a proven track record, but you are some guy off of the street claiming that he can build his own house. Think of it from the paranoid banker point of view. If you give up or bail mid-project, what value does it have to the bank?

Good call on the precast though, concrete homes are amazing. I helped my in-laws build one out of Ecoblock (stacking styrofoam block forms). Not only was it fairly easy to construct, but the insulating ability (both sound and thermal) is amazing. Heating and cooling their nearly 6000 sq ft home now costs significantly less than their previous 2500 sq ft home.