You CAN make the floor out of hardware cloth, but that doesn't mean you SHOULD. While I'm no expert on chicken crap, I have seen enough of it to know that 1/2" hardware cloth is not the floor I would go with. A lot of the crap, more than you would like, is going to just sit there on top of the h/c floor. They (the chickens) put out for the most part, poop that is larger than 1/2" square. I imagine you could blast the crap through the screen floor with a strong water blast from the hose. But then you will have a stinking, watery crappy mess under your coop.
Go with a solid floor, with some kind of bedding on it, like pine chips or sand. With three birds, it should be easy to keep waste under control. Also, raise the coop up off the ground. Getting the coop up off the ground allows you to see whats going on under there, as far as any pests go. As in rodents, snakes or whatever.
And welcome to BYC.
Jack