Turning Pink installation at W/ Project Space in New York by Leong Leong Architecture - Made from 3inch rigid insulation and mirrored acrylic this temporary and site-specific installation was part of a series that ‘explore the translation of a legible figure into a continuous visual field’.
VMZINC's Structural Roof is a construction system combining a standing seam roofing in VMZ Zinc plus with rigid mineral wool insulation laid on supporting structures in steel, wood or concrete. It's a modular warm roof system for any type of deck (steel sheets, wood, concrete), suitable for low to high hygrometry, that can be used in all types of roof.
After some advice from MAO members, I tackled this yoga ball project. I used rigid wrap for the first layers of solid surface, then filled the inside with insulation foam. Now I'm doing the thinset/mesh treatment in several layers and then it's ready for mosaic!
It's certainly possible to install a layer of rigid foam on top of a concrete slab, followed by a layer of plywood. People do it all the time when they remodel their basement. However, most people wouldn't call this solution "simple and cheap" -- two adjectives you mentioned. If you decide to go this route, pay attention to the continuity of your thermal insulation at the perimeter of your house, where the floor foam meets the walls. Otherwise you'll end up with thermal bridging at this…