I had several of my snakes in the basement, moved them upstairs.

Sounds like a challenging project. Use an area away from the utilities, seal it up so the animals are not breathing the bad air from the furnace, and you'd be set.

Are the foundation walls poured or stacked stone? is there ways in or out? (for escaped snakes)

Take pictures of the process start to finish

One day I'd like to go back down there, since our basement is 25 x 50 with an 8 foot ceiling, But I would like radiant heat, and to build a 12 x 12 enclosure / room for a burm.

Setting up a couple big livestock tanks, one for "wogs" and one for minnows. Basement is the best option, strongest floors.