How much are you willing to do? Do you have cash for repairs after the purchase? Any reputable contractor will have a hard contractor with everything spelled out, the only extra expenses will be if you change things or go over budget when you pick out flooring, light fixtures, cabinets and things of that nature. Your foundation, framing, roofing, rough plumbing, windows and things of that nature will be set in stone, if they loose money on the work thats their problem not yours. If you are your own general you will save $40-60, 000 by finding your own subcontractors and over seeing the work. If you are handy you can also save a lot by doing little stuff like trim work, mounting/hanging cabinets, insulating/soundproofing interior walls, painting and whatever you feel comfortable doing that a warranty isn't a big deal such as roofing, foundation, hvac.
If your buying used you need to consider how much work is needed and how soon. If you're going to need hvac, windows,or roofing you need to consider that part of the cost, these are very expensive necessities that are better of being part of your mortgage than financed down the line if you cant pay cash. Are you willing to live with other people's taste in flooring, cabinets, and the like so long as they are in an acceptable condition, if not might be better going new.
We are willing to cover any cost if necessary and yes we do have the funds for repair after purchase. If we are buying used we are going to find a home that is ready to move in. If we do purchase used, the only thing we would really do is just re-paint the interior and shampoo the carpet. The homes we are looking into buying are in a gated community and the homes are nicely well kept indoor and out so there wont be too much to fix. The homes in our area of interest are very modern and were all custom homes when they were built. No two houses are the same on the block. We are pretty handy and love to do DIY projects, but my dad would rather pay someone to get everything done properly if we do build our own house.