You’ll be able to find the bill of materials, STL files and other information on the github page.
There are currently no comprehensive build instructions; here is an album of the first RepArm prototype built. Unfortunately, for some reason, the album is completely scrambled. If you want to build your own, it’s quite straight forward – look at the assembly files, and even without them, everything fits together quite obviously. The only thing to keep in mind is that the belts are a bit tricky to get in place if you don’t do it before you assemble the x and y carriages. Put each end of the belt in the belt holder, assemble and then tension using the threaded rod on the x axis and by sliding the idler outwards on the y axis.