Sometime ago I sculpted a bas-relief Cthulhu tomb sarcophagus lid around an intersecting triangle pattern, again it's the weigh up between what I can achieve and what goes on in my head! Marking out the same shape onto the foam I then cut using a metal saw blade to avoid ripping up the material too much. To break up the outer lines I used a fine tooth hacksaw blade and marked out some semi-circles for removal.

The back edge of the base piece is angled backwards, I'm hoping this will act as a cantilever support for the mausoleum, although I've got some thin MDF which I can put right through the back piece to assist with that if needed. A good bead of no nails to hold the 2 pieces together is now required!