It worked fine for me, nice idea too, obsidian so creepers cannot blow it up and an automatic one way door.
What you could do is build a large platform, high in the air, above some water (make sure it's 2 squares deep)
Build it out of half slabs so mobs cannot spawn on it.
Well I've started my jungle tree house. look for the abnormally tall trees at the edge of the jungle near the village.
ok, knowing a bit of the map is a bit like cheating, but I've not gone diamond hunting and marking out the biggest patches or anything.