I think Section 8 will still consider an adult child a dependent, if that person is still in school. 

But Im not saying I wont consider an FHA/VA loan and put the 3.5 - 5% to get a deal.

To consider an allocation to deduct the old roof you would have to do some research under the Tangible Property Regulations that would allow you to break out the remaining life from that portion of the building.

If you get bigger than that, you need to consider an LLC for asset protection. 

Major systems like HVAC and septic must be in working order.If any of those items cause an appraisal to fail, you can consider an FHA 203K (construction) loan. 

Most lenders don't consider an after repair value, and most appraisals don't list an after repair value, which makes me think you're not applying for a conventional loan.Did you already remove the appraisal and / or financing contingency before you got the appraisal back?

Also @Tim Porsche spoke of an ozone generator, also consider an Hepa filter air purifier.

The downside to them is that they would not get to participate in the overall profit of the project if it all goes well, but of course they also have less risk than everyone else.If they want in as equity investors, you should consider an LLC or a Limited Partnership (with the LLC as the general partner). 

Might consider an estate plan as well if you don't have one in place already.

Also, sellers usually won't even consider an offer without at least a preapproval in place.