Awhile back we talked about OpenSPIM, which has a great step by step tutorial on how to make a light-sheet microscope.
In the same vein there is Open Spin Microscopy, a website with several DIY light sheet microscopy projects including a much simpler optical tomography design.
The website can be a little tricky to use, and much of the information you want is actually accessed by clicking on the “Sub-Systems header”. However if you get things built, then much like OpenSPIM the software to operate these devices is open source and designed for Micro-Manager which is nice and easy.