Inspired by Jason Casteel's TARDIS Prime artwork:
I saw the shirt, and had to work out how to make it actually physically work. I did end up having to completely design the transformation sequence from scratch.
This print can be assembled without glue or any screws or other non-printed hardware, although you may want to glue some of the parts together anyway if you intend to actually play with it. The only challenging part about this print is the large number of parts (over 70 individual parts needed) and the size of some of the parts (although you should be able to handle everything with a 100mm cube print space).
It's a big toy once printed. Tardis mode is about 6 3/4" tall and 3 3/4" wide. Robot mode stands 13" tall - it's folded up pretty tightly when it's a Tardis, unpacks into a much larger toy in robot mode.
Honestly I'm not completely happy with the way this turned out. It's large, took a lot of plastic to develop, and the robot mode is incapable of standing on its own. It's too large and top-heavy for the friction in the joints to keep it standing, even though the feet are huge. I may attempt to redesign the entire toy at a smaller scale, to be easier to print and more functional as a display figure.
This was printed in PLA on my scratch-built Delta style printer. The original files were drawn by hand in AutoCAD. I have uploaded a zip file containing all the AutoCAD source files.
My blog, with information on this and other things I've made, is at drewsrobots.blogspot.com/