Step 2: Gather Materials and Tools.

Styrofoam ~ Free (This is trash, you can find it for free. It's used to pack all sorts of things. Try going to the back of an electronics store and asking if they've got any you can save from the landfills. I used a broken styrofoam cooler and some odd packing bits.)
Grout mix ~ $8.98 (I got a carton of Sanded grout mix in HEMP color. The sanded leaves a rougher texture than unsanded. The hemp is a kinda dark gray color that already looks like rock. It gives a nice dark base color and could be used without coloration if you want)
Cement Color ~ $4.96 (I used Terra Cotta. Mixed with the Hemp grout it gave a nice red rock color. This is a liquid color mix. You can also use powdered grout color mix. It's about a buck cheaper, but they were out of the color I wanted.)
Great Stuff Expanding Foam Insulator ~ $5.00 (Trust me, this stuff will make things much easier and is well worth it)
Water ~ (To mix the grout)
Water Based Polycrylic Satin Sealer (Go for Satin, not as shiny as gloss and gives a more natural look. You'll need enough for 3 coats. A small can will probably suffice. )

Knives and hand saws (to cut styrofoam and shape your cave)
Hot Glue Gun and glue sticks (works great for gluing pieces together and it's safe. DO NOT USE SUPERGLUE. Superglue, or other such chemical glues will melt/eat through styrofoam and give of toxic fumes)
Bucket (For mixing grout in)
2 Cheap Bristle Paint brushes (One for applying grout, one for sealer)
hey man awesome job just wondering if this is water proof i want to make a water fall for my red tail boa out of the same stuff

making an aztec temple for my redtail it works well, and if you use the clear silicon (pasti dip) it will waterproof it. (using that ontop of the joint compound because i want to seal down the moss im putting on mine so my snake doesnt pull it off :) )