For a tree frog your going to want taller its not hard taking a fish tank and standing it upright and doing a vertical conversion. The first tank I made was a vert, and there are tons of posts on here explaining how to do it.. As for keeping it clean if you spray the tank with D/O water you won't have any streaks on the glass since there are no impurities in the water.

You can get D/O water by the gallon at Walmart I think they call it Reverse Osmosis water though