That size cage will probably be too big for a hatchling burm (baby snakes need to feel secure and actually do better in the confines of smaller enclosures for the first 6-12 months). I would start the hatchling off in a cage that is approx. 36" x 18" (like a neodesha, vision, etc.), then, once the snake outgrows that cage, consider making something that will be his/her permanent enclosure (you will want someting at least 6' x 3' and preferably larger).
On a sidenote, in terms of your design, I would recommend something not quite as high....2-3' is more than enough and will allow you to better heat the enclosure.