Add Sewers or Water to Buildings

Right now, have to inverse the building of rooms on an flooded plains to create a sewers like space, but it's very plain. No ledges, gates, etc. Would love to see a Sewers style terrain, or the ability to add water to buildings and control the water levels through a slider. Could even just be a new "room" which is a sunken floor, water, and thin ledges if enough space along the side.