jenn, I just got approved for the Fannie Mae Flex 100. My scores are mid 600's, but they looked more at my DTI according to my broker. They also like to see some assets, so if you have some funds sitting around in a supplemental retirement or anything similar it will help a lot. I actually had to come up with the closing costs, only around 3%.
The good thing about building a new home is they will start with little money down. TIP number 1... New home sales are down. As long as you get a preapproved letter from a lender you are all good. Key work PRE! The builder will ask for earnest money and most want 2,500 plus but they will take 500 bucks. Lots will do zero. Your goal should be zero.
Now all contracts have a way out but you may not get your cash back. Most contracts will state that if you get turned downed by the lender you will get your money back but the lender will need to provide a turn down letter.
I have a friend just started building with ZERO down and got a free TV.