The default Prusa Mendel build is easy but has serious flaw. The 60/60/60 rod system at both sides may make the printer strong, but it will block the X-carriage.
Because the stepper motor sticks a bit out the carriage, it will reach early the end of the X-row.
And there is diagonal rod in the way. The flaw with rod by X-max will limit the X-max much more, but it seems also limit the Z-height too much, because more higher height, the lesser the room at X-max side thanks to both diagonal rods.
This is not good. You will never have full height over full X and Y sides.

To solve the problem, i have examined the X-max problem. It's clear the part of the rod must removed to give X-carriage more room.
Many commercial and improved Reprap printers don't use 60/60/60 rod system, so the X-carriage has no blocks at X-max.

I have designed the new frame vertex part to solve the problem. I have just tested on my printer and it's greatly improved in X-max and Z-height. Now i have almost full 187x187x100mm print area. (some ppl may have full 200x200x100 mm area).

Because just two parts are changed in default Prusa Mendel build, this is really easy solution and might done in just 10 minutes re-build. Printing is around ~2 hours on slow printers.

You remove the old frame vertex at right side (x-max side) and place the new frame vertex in the same place. The rod must shortened until it has minimal 23 cm long length. This is enough to use rod again with the new frame vertex part. Don't forget re-check the dimensions to avoid small offset if you have all mounted.

The new frame vertex seems also solid enough. I have "bridge" version used in the design to keep ABS usage low, but keep it strong as possible.

Oh, my printer is Prusa Mendel v2.
The part is designed with Google Sketchup.
See the pictures. Have fun with printing bigger models!