What do investors use for the moisture membrane(s)? 

We recently had a flip where the membrane over the garage was leaking on the north edge, water migrated back about 15' before finding an opening in the decking and dropping through to an interior hallway.

. $1,520.00•Demo about 12” of walls and rip out entire shower pan and step •Install cement board on exposed wall •Apply RedGuard and Waterproof membrane to shower pan and up the exposed walls •Install new drain adapter in shower floor •Install new tiles provided by client Optional (just in case fixing shower pan does not fix the water leak) rebuild shower. costs extra $5100•Demo shower • New plumbing for a new fixture •Install cement board on exposed wall •Apply RedGuard and Waterproof membrane to shower pan and up the exposed walls •Install new drain adapter in shower floor •Install new tiles provided by client •Client provides plumbing fixture

If only the outer roof covering (membrane, shingles, etc.) was replaced but none of the underlying roof system, it is not a restoration and you can expense these costs.  

Is the membrane secured to the parapet wall correctly?

Some will go with a nicer pad and a cheaper carpet.The nicer pad makes the carpet FEEL more expensive to the tenant when they walk on it.A great pad also resists wear and tear and if you need to replace the carpet the pad usually can be used again.Used to you would put a plastic membrane in between the carpet and pad to protect the pad but the plastic would slide and make noise sometimes.Now they have pads with built in protection.You are not looking for the cheapest product but the best VALUE for what you pay.It depends on the area and what kind of tenants and rent base you are working with.

Bottom line a roofing company isn't going to typically pay for punctures to the membrane of the roof like a roof mounted a/c unit.

I’m an insurance agent across all 50 States and just verified with another colleague that this type of roof membrane would be acceptable for insurance.Quote from @Patricia Steiner: The coating isn't acceptable for insurance engagement on residential properties.   

Ross Hamilton (or whatever this nasal tone, sleazy little self described: "ex dumpster diver's" real name is?)

Whenever you install tile over concrete an uncoupling membrane must be used to isolate your tile/ grout from the possibility of a crack in the slab ruining your floor.