Also, if they have foundation wall cracks, I would use the waterproof membrane they can provide to cover the walls.

I usually will put up a vapor barrier over the studs, then concrete board or green drywall, then I use a waterproof membrane such as Kerdi.

The flat roof is also almost always going to be a single-ply membrane material not a standing seam roof because its much cheaper and no one is ever going to see this part of the roof except if you're standing on it. 

Account Closed the prostitution red latex paint sounds like Red Guard waterproofing and crack membrane sold at home depot. 

It allows you to form slopes with it, then you put your membrane on top of that once it's dried, then you do a final slope with the same mixture, then you tile it.

He'll remove all vents and roof jacks, and replace with new.Second contractor will remove existing roofing membrane down to wood deck substrate. clean, apply1 layer #15 lb base underlayment, install Malarkey Highlands laminated 30 year asphalt fiberglass shingles, seal all roof projections, ground clean up and haul away for $4524.( http://www.malarkey-rfg.com/PDFFiles/MRP%20WebFliers/HighlanderFlierWeb.pdf) Highlander-CS™ ~ Malarkey's 30 Year Laminated ShingleBuilt with the strength of a highland castle, the Highlander protects your home while providing distinction, security and value that is prized by today's homeowner.

If you don't want to go that route, there are waterproofing membranes that you can apply to interior concrete/block, but keep in mind the hydrostatic pressure of water in the ground can be tremendous and will eventually find the weak spots of this approach. 

Adding the tub in my opinion adds value especially to those that may have young children, or when you need a large area to clean large items.Tub & tile- usually there is greater surface area (tub walls and ceiling) to tile so your costs of tile will go up, for the tile, the concrete backer board and the membrane.

I was told by two roofers that membrane or rubber roof is my only option because of the roof pitch.

The layers he's referring to is the insulation below the membrane.