My A. avicularia recently moulted and outgrew its old container, so I built a new terrarium for it. And what better way to decorate it and keep up the humidity than by planting tropical plants. The N. sanguinea is sitting above a small rubbermaid container with drainage holes about 1" above the bottom. To keep things moist I will pour water on the sphagnum around the Nepenthes. That will fill the "tray" and excess water will seep into the surrounding soil for the U. longifolia.
The tank itself is built out of 8.5 x 11" sheets of plexiglass. These used to cover plaques, and they conveniently have holes in each corner. Each plate is fastened to a frame at the bottom by small nails and spots of glue. At the top corners they are held together by wire. The bottom of the terrarium is wood; I covered it with a square of 6 mil plastic and sealed everything up to soil level with silicone. The lid is a wooden frame with chicken wire and I added a pane of plexiglass down the middle to keep up the humidity for the spider. Since arboreal tarantulas often like to build their webs up against the roof of their tank, I cut the wire on one side of the lid so that a flap can be lifted up for feeding.