I've been looking at a number of hive plans online and in books while always trying to thing of bee space. Today I took the plans from this site for the hive bodies and frames and sketched it all up in AutoCAD to see how it all lays out.

The Langstroth hive plans call for inner dimensions of 18 3/8" X 14 3/4". The length is good, as then the Dadant-style frame plans are about 1/16 away from the edge of the rabbet on either end. Now, with the frames evenly spaced that way there's just under 3/8" between the side bar and hive body. Maybe that's why the plans call for cutting the hive pieces a smidge over?

Now, about the width of the frames in relation to the hive body. The width of the sidebar determines the overall width of the frame (in top-down view).
With 10 frames in a box, that's only 13 3/4" across when all the frames are tight against each other. What about that extra inch?

I think I see that setting all the frames a smidge apart from its neighbor and the hive walls puts the top bars at about 3/8" apart from each other. Is that the way it should be? I've read that some people even cut their top bars a tiny bit more narrow to increase that space for ventilation. Good idea / Bad idea?

In the end I think I'll be buying all my frames and making the hive bodies, so perhaps I should get all my frame pieces and then build bee-space boxes for them?