Building a home-made enclosure

[red_tail_ale]

So, my red-tail boa is beginning to grow. Right now she's about 4ft long and lives in a 36"x12"X24" tank.

Unfortunately, she's beginning to grow more. Rather than keep making a new cage, I decided to build a cage to accommodate her up to 12ft.

I have a few ideas. I've been told boas are semi-arboreal, so I want to have the enclosure be tall too. She's an avid climber so I'm sure she'll enjoy this. My current plan is 7'x3'x4' (4 feet tall) bi-layer, with one side containing a basking lamp (on a timer) and the other containing a hide. On the lower level it will be relatively cooler, with a cool hide and a bath. In the center I'm building a three pronged false tree, with a prong running vertical and two lower prongs making a "step ladder" design. Along the bottom I'm planning to put heat wire beneath the padding. This will be at a lower wattage to ensure belly-heat safety and to keep the top of the enclosure warmer. The whole enclosure will have an overhead ceramic heater on at all times.

I plan to have the front covered with plexiglass which I will latch using magnetic strips as well as outer latches. The glass will open out like a normal door. There will be air holes drilled at the base near the cool side as well as a few in the bottom of the back to increase air flow. I'm placing a humidifier either in the enclosure or leading into it. As for the floor, I'm still undecided whether to go with Cyprus Mulch (which I use currently, treated for mites), linoleum tile (I've heard retains heat well) or roll-out padding.

Right now, I have a few questions.

*What is the appropriate kind of wood to use? (I know cedar and pine can't be used)
*Should the wood be treated or sealed?
*Should the heat wire run along the bottom or along the sides, and should it be put on the outside or the inside of the enclosure?

*Any other suggestions or do's/dont's would be greatly appreciated. I just want to ensure she'll be comfortable in this tank from now until the time she's fully grown.

I've included a sketch, since my descriptions aren't very clear.

Thank you!