Completely gutted house and estimating rehab costs

[Jonathan McClintock]

I met with a guy yesterday who is selling a house in St Louis. He has completely gutted the house, roof is only 1 year old, inside is just studs. There is a "newer" electrical panal, but that is basically it. Will need all systems . . . will basically need everything. House is only approx 900 sq ft (2b/1b) with rough in for another bathroom in basement. How do I begin even determining cost for that or is that the kind of rehab a beginner like me should just avoid in the first place?