Often times lightwells and roof membranes can be punctured by installations without the proper water proofing.

Bought a foreclosure with a wall that appears to be made up of 2x3 walls sandwiched together with some weird hard plastic membrane between them.

You can add another layer though and make it a pseudo three hour wall but you need to add a sound proofer membrane between these layers.

Scopes will include repair of flat, membrane roof, repair of brick veneer, electrical, potential foundation repairs.  

My park is in an area that occasionally get 15"-20" of snow.My options seem to be:1)    Just add an EPDM membrane to the existing flat roof. 

If it’s more than that, The best waterproofing is to dig down from the outside, add waterproof membrane to the exterior of the foundation, then add some drain pipes on the exterior as it’s back filled.

I should have mentioned the membrane systems.

But the 4 points and wind mitigation inspection report show it is membrane roof rather shingle.

If I put thinset down do I need to put some kind of membrane down so it doesn't drip through the planks?  

And FWIW, not all older, aging roof membrane coverings at or near the end of their serviceable life qualify for a silicone roof coating or a recover using a single-ply roofing system whereby a complete tear-off and replacement often remains the only viable, not to mention most expensive, option available.