Well, for one thing, make sure your case is the form factor you want to use. I.e., dont get a Mini-ITX motherboard and construct an ATX form factor case. 2nd, make sure it has space for all of the ports you want, the basics would be space for one USB 2.0 and one USB 3.0, a mic jack space, and an audio jack space. I would also make sure to make cutouts for the PCI-E backshields, the I/O shield space, fan space and grills, and power supply cutout. make sure all of the parts of your case match up, so the side panel isn't a few centimeters too big for the case and things like that. Confirm you have all of the materials you need before you build it, including plastics. Also, try to make the case look cool. I know that is it difficult to do this in metalwork, but try to make the face look cool, maybe add some metal spikes or a kind of "face" design grill on the front. Last, make sure that the power and reset switched all have cutouts. Before you actually start making the case, I would get your parts and decide what you want to go where and what power, reset, USB and jack components you are getting. I dont know where you can get these components, but my best bet would be to look for industrial computer component manufacturers (the boys making  components for companies like Raidmax and Coolermaster) and see if they can get anything. Good luck! :)