I have on occasion found when you get ice buildup on the roof the north side can form dams and you have water go under shingles and run into the ceiling. 

As party due diligence check for lead paint and asbestos siding and shingles as well as on the inside (tiles, insulation etc)Abating asbestos can be very costly

Example if 1500sf roof needs to be replaced you know in your area it will cost you $200-225 square you are taking about close to 5-6K, but as a wholesaler you show as re shingle in rehab estimate @cost of $1500, that is not doing justice to investor, I have seen 20 properties in last 2 months ,I purchased 2 of them both of them are going to run $10K more than their estimate, luckily both properties are in excellent areas , I will still make my margin, keep in mind I am also new as investor in Orlando Florida, , in Alaska we had several properties buy and hold , so I am learning too.

.- new kitchen (countertops, cabinets, sink, DW) in one unit $5000- asphalt shingle roof about 20 yrs. old $6000- exterior paint (garage, rear porch) $1000- refinish hardwood floor (one unit) $1500- interior paint $1000- one unit's boiler (looks original!)

-The roof will need replacement soon, some of the shingles are already curling up pretty good and while it could probably at the very most hold out for a year, it should really be replaced asap, certainly before another wonderful WI winter hits!

The wood shingle siding needs repainting.

I'd walk if I didn't have either the cash or the equity after I bought the place.If I got past the above, my next step would be to do a daytime drive-by on the property and see if there were any obvious signs of major repairs needed (a roof with waves in it or damaged shingles, rotting fascia, stress cracks on the exterior, if the house is square with the foundation, general condition of the exterior).

The only difficulty is finding someplace to hang your shingle.

I have used a few tools on the web that estimate costs by your zip code - i was looking for the links but I no longer have them - they are only estimates but do give a ballpark - your home insurance company has their own methods too - but you absolutely have to get down to the absolute details of materials - like a roof estimate that I did - the kind of soffits will make a difference, the kind of shingles will also tell you what kind of valleys you can do or not etc etc - you need to aquire either a lot of information or a trusty contractor to do this!

You don't have to be a master contractor to see if a house sits crooked, if the foundation has cracks, if the roof shingles are curling, if the ceilings are water stained, etc.