36" x 18" of floor space (ie a "40 breeder" tank) is the minimum recommended
size for an adult beardie. Height doesn't matter so much, 18" to 24" is plenty.
Bigger is always better though. I keep my dragons in the equivalent of 75 gallon tanks, although they are custom made and have sliding glass fronts rather than being solid.
Just make sure to avoid the "55 gallon" tanks that you find quite often on craigslist and such. Those tanks are usually 48" x 12" which is great on length but isn't wide enough.
Not sure he likes the new basking setup, the mesh is A LOT denser in this one, I have a tube and a MVB for basking, but he seems to be trying to get closer all the time, spends a lot of time like this:
Is he just adjusting to the new viv? I figure it'll take him around 2 weeks, like when we first got him.
Difficult to put the lights inside because of the limited height.