Michael Colombo from Make wrote a guide that goes through the steps Michael uses to build acrylic enclosures. When you are finished a project you may be lucky enough to make it fit into a mint tin but for those other ones that need something a bit more custom why not make an enclosure that is just as hand made as the electronics inside.
“When building your own creations, it’s sometimes necessary to bend the acrylic sheets themselves in order to serve your vision. This can be easily done using little more than scrap wood, a Dremel, circular saw, heat gun, and a vise.”