i would probably get rid of the rolling metal door on side of the house. imagine some zombies banging on the side of that thing- it would probably make tons of noise (which would attract more zombies)
If you read "The Zombie Survival Guide" by Max Brooks you will see there are flaws in that design. They also don't say enough about sound proofing (zombie moans can drive you insane after a while), renewable water source, silent electrical generators, etc...