Just playing devils advocate here..........I agree with what everyone is saying about filing a forgery report with the local police and contacting your bank.
However, is it possible that the materials truly are on backorder and he had to put money down with the supplier to place the order? Is it possible that he is just unreliable at getting back to you but is waiting on the materials?
I would also consider asking him who the supplier is and attempt to verify that the materials have been ordered. I have seen some items take a long time to come in. My co-worker recently replaced his deck with composite materials and had to wait for an extended period to get them in.