We are remodeling a shower in a 50+ house. The current shower is a dark hole. There is a concrete floor and fiberglass walls. We wanted to expand the shower by width but cannot by depth. The house is on a slab so the plumbing will not be moved. What is the best and most cost effective way to do this? Should we frame and tile with a glass door, cultured marble bottom only then tile, culture marble all of it, or use a drop in (worried that it will not match standard measurements)? We need advice.