In 2006 I bought a home built in 1999 and the coil went out during the first year I was there.  

Recently I had an evaporator coil go out in a 3 ton Goodman AC unit.

The coil froze up - the wife was blaming me - after they lived in the house for years.

If it is a metal shed then they have to remove it when they move out. 

I've also been investing in real estate for 55 years.When a property has a raised foundation the sewer and drain pipes don't concern me because we can replace the entire water and drain system in one day.The problem with a concrete slab is cast-iron drain metal is porous and looks like it is full of air pockets.

A swing set I would not worry so much, if it is a smaller metal one I would get rid or it or just offer to get rid of it or let them have it.

If your property is a 2 story brick structure with slate roof that is what it needs to be insured as, not as a 1 story with a metal roof. 

The images I saw on quick search has OSB outer layers but I read that it can be sheet metal, concrete board or others.

My liquidity in 2018 went into the precious metals market.

Installing a traditional a/c would either be an air handler or a furnace with the ac coil on top and an outside condenser both options would need duct work.