Just curious. Why would you have to pay penalty. (presumably for walking away and losing your deposit) for a house with that much damage? Did a typical 'home onspector' find the damage you mentioned (foundation, gas, plumbing, roof? If yes, I would bring in an engineer to review home structure and systems. More detail will help you, especially if Seller is paying for repairs and may nickle and dime you for every icontractor line item (a roof with exact same shingles can be installed poorly and last 5 years or installed correctly -- underlayment, flashing, proper ventilation, etc and last 20+ years).
But it's your call. If you provide a bit more detail (such as: Foundation-needs this; Plumber: new gas line to fireplace and dryer,and new water heater; Roofer: new roof due to age, leaks, hail damage), I may be able to help. You may also save some $ by hiring individual contractors vs. GC, especially if problems don't 'overlap' each other (plumbing work in foundation area). If problems are specific, GC will just add 20% to your cost.... more