How Can I Get the Half Gable Roof's to be Even?

I'm assuming those two roof pieces aren't the same width? To fix it, you'll probably want to hold Shift while manipulating the peak eaves to remove the eaves on just that side (where the two pieces meet). If that's not enough, you can hold Alt while adjusting the height of roof pieces to get a bit more precision. (If you want to see what it all looks like, you can look up Sahmandbean on Youtube. Her old roofing tutorial videos are really nice.)