I finished the structural work/hardscape on my terrarium recently. It's 4ft x 18" by 21" tall.
It's got a couple plants in it but needs a TON more. I'm waiting until after my vacation in May to finish ordering plants to fill it up.
I took a couple pictures that show the hardscape really well. The left side has a running waterfall and pond area.
Hoping to grow some nice orchids and house some dart frogs







The buildup pics are not all online yet, but here is where they are:
http://i.ugtz.com/gallery/75g-Viv-Construction

here is my only other terrarium to date, a 10 gallon tank:



I highly recommend this hobby. you get greenery all year, it's low maintenance (except watering, which can be automated), and if you have kids it's a fun project to work on together.

I highly recommend this vendor:
http://www.blackjungle.com/
they are located in western MA and have an AMAZING store packed full of mature terrariums housing dart frogs. They are fun to visit and have the best stock of materials, plants, and livestock in the entire USA.