There is a building not in use, but is there plumbing and electric?

You need to make sure there is room on the electrical panel to add larger appliances and also plumbing is easily accessible (to keep costs down). 

Does it include plumbing and electrical? 

Whether it is the trained and licensed professional in real estate, inspection services, septic, plumbing, electrical, HVAC, etc..... we need them so organize them in your target area and jump in...  

And yet, you might be surprised how much foolishness you’ll uncover if you peel back some onions… one thing that I learnt from all these syndication mistake that is that before joining "such private club" is that "I thought I know most of the risk but I found out any investment project (even outside typical syndication) can fail to some unknown circumstances"......from plumbing to comps ............ there're just so many that i don't know. 

This depends on the neighborhood, material/finishes, custom touches, new roof, HVAC, electrical, plumbing, and ARV.

About $250 to $300 per square foot, because it is small which drives the per sqft cost up absorbing kitchen, bathroom, plumbing, electrical, utilities, basement, roof and impact fees into a small footprint.

Owning a car wash means you need to know plumbing, electrical, mechanical, and when to call the experts.

It could be an easy fix like this or a bigger problem depending on the factors at play (are the joists accessible, will it mess anything else up if you just jack it up and reinforce, is there water damage or structural damage to the foundation causing the sag instead of just old joists, anything else going on like a supporting wall or posts under the floor, wiring or plumbing runs involved etc.).

As long as everything works (lights, plumbing, etc.) and there are no hazards (like an open ground) the big things are peeling paint (particularly on window sills) and smoke detectors.