Most of my cab is a modified version of Russ Prince's very handy layouts available on his site. I modified the base somewhat, as I found he had a large footprint, and I went impromptu on the keyboard shelf and speakers and stuff. All of these mods I was able to do easily in Corel Draw (yes, what a great drafting package... heheheh).
The control panel, though, is a different story. I've just completed my 6th control panel in 3 years, prompted by the fact that I finally scraped together enough $$$ for a happcontrols trackball (yay).
I finally have a repeatable process for what I consider flawless control panels. Amazingly, I also do this in Corel Draw! The horror!
What I do is, I have templates that I've made with exact hole size and spacing for buttons, joysticks, trackball, etc etc. I have a 8.5 x 11 sheet full of buttons at an exact spacing (I think 1.5" on center, but YMMV) so I can cut out groups on them in any configuration and keep the spacing exact.
So what I do is, I have this large roll of graph paper (1" grid), it must be for presentations because the back has post-it glu on the top and bottom. It's the perfect size for me to roll it out and stick it on my board, and lay out all of the templates precisely where I want them on the grid. I can feel it out, do some imaginary motions, see if the config all works... and if so, I just tape down the templates, take it to the garage, and drill away. The result is flawless, with everything pleasing to the eye and the hand (as all things should be).
Anyway, like I said, it's what works for me, YMMV.
Chemame