Be sure to convert to shingles if possible.- Accessibility - if they are out of code, you will have a very bad time pulling permits - including most value-add opportunities.- Sub-metering.

(loose or missing shingles, roof maintenance, loose gutters, and such...)There was no charge of working on the stop sign (and shouldn't be!) 

Pitched shingled roof, 2x6 walls, 1/2” sheetrock - same materials as a stick built.The cost will be 1/4 to 1/3 of what a stick built would be but I’ll be able to get the same rent for like square footage.

Not only will it last you twice as long as a shingle roof, it will  cost less on your insurance every year.

As far as the roofs go, they are 30 architectural shingles about 10 years old, but are installed over another layer. 

After we purchased I got my roofer to the property and it turns out that not only did it have the top layer, it had two layers under it and the bottom layer was cedar shake shingles. 

I currently have enough Vynal flooring, Roofing shingles, appliances, electrical items for the whole 4plex build.  3.

Was  the leak caused by 40 year old shingles coming off or a 95 mph wind? 

But I wouldn't ignore a cedar shingled vintage Nags Head house that has already survived years of brutal weather.

And what shingles did you go with?