Smooth rods and diagonal rods length dimension -Rostock

Hi

I´m trying to build a Rostock, and i have doubts on the dimensions of the rods and the resulting printing area.
I have 500mm smooth rods, and i wanted to ask how can i determine the diagonal rods length and the resulting printing area?

If possible i would like to get something arround 200x200x200.How can i see if its possible to get this printing envelop?