@Dean Gittings i have sheds on a couple of properties and the lease says “sheds are not warrantied to be water tight or pest free.” or something like that.

And if water is getting on top of the sink, water could be leaking through the faucet pipe openings in the top (assuming the gasket or plumber putty isn't watertight enough or missing).

The door travel can be adjusted and they will never be water tight.

Here they are:sell in its current shape (probably expect to do same, worse, or a little better than you paid)sell in its current shape with CAD plans and a vision for what the place will be, with some thought on the development side (probably some volatility here but the idea would you'd position yourself to do much better than #1)Do the development to get the 'shell' solid, water tight, and leave the systems/final build-out to a developer that has more experience/time/capital to execute down the stretch with the rest of the Engineering, tenant readiness, or whatever (higher risk that 1 and 2, with most of that risk being from what you've described on the structural side of things) - There'd be some real money here, to get here and I wouldn't be 100% confident you'd get your money back. 

If we replace them it would be just for aesthetics, the windows seem to be functional and water tight.   

Sometimes the exterior trim will need to be caulked to make it water tight to ensure this does not happen.  

The PT plywood alone would be tough to keep water-tight. 

I think next time he'll make sure if a side of roofing is ripped its water tight before moving on to limit any damage!

Before you even think about bidding on this property, you need water tight diligence knowing what is going to happen with this lagoon in 2019 from the city, county, state authorities.  

The problem will be that if it flexes that grout lines will crack and the backsplash wont be watertight.