A typical ceiling might be double 5/8" drywall, resilient channel, fiberglass insulation between joist bays with 3/4" ply subfloor.

If in ground is it concrete, vinyl liner or fiberglass? 

My choice as the owner of the property is to install a fiberglass or acrylic 3-side surround direct to the studs.

One we replaced the tub with just a 4x4 shower base The other unit had a bigger bathroom so we put in a nice solid fiberglass Kohler tub I grabbed SOR from Lowes cheap.The tenants with the two little kids took the one with the shower stall & the Vegan millennial couple preferred the tub setup. 

I have an otherwise nice lower B class townhouse that has the absolute ugliest fiberglass shower surround ever produced.

I am guessing this is a plastic or fiberglass tub. 

@Greg Jeanfreau fiberglass tub with caulkless interlocking surround.

Insulation passed the building inspection but one thing I know now is to make sure the roll out insulation is down but in my situation the blown-in fiberglass was basically in a lump in the middle of the building and was never layered out to the edges.

It is true that stand alone showers can be made to look nicer, but they also cost a lot more to construct than a fiberglass surround. 

I’m just going with fiberglass shingles because that’s what’s most common in the US. - First thing I do is take a little corner of a shingle and twist it to see how brittle it is.