Does this sound like a good cat house, and how do I get feral cats to go inside?

You should probably build it out of something a little more sturdy if you plan on keeping it around. Feral cats are wild.. they do what they want. They aren't the same as a "stray" cat which happened to wander out of someone's house. Ferals haven't had any human socialization.. nor do they want it. It's like seeing a squirrel in the yard, basically. I know you're trying to help them out, but they're smart and know what they're doing for the most part. You can't force them into the home you built, but putting food inside will usually draw them in. What you should be doing is buying a humane trap and taking them to a local lost-cost spay/neuter clinic so that they'll stop having kittens! We need to slow down the animal population.. the shelters are overcrowded. After they're fixed, release them back out where you found them.