I think a level 2 should be 4 bricks high and a level 3 sent 5 bricks.
I'm not the one to size, I don't have the .blend files for the bricks. BTW where can you find them?
I like anybody's sentry better.
In this case, anybody would want to model the 2 and 3rd. I would love to model the frist though.
Off-topic: What do you think is wrong?

I was really tempted to model the lvl one sentry.