As much as I like Vivian, and I think ALL of her books need to be in all our libraries (by the way the DVDS are on sale at her website) the matcutting book shows multi opening mats, but doesn't give a step-by-step of doing them.
Robb, everyone will have their own method of doing things - and this is mine:
Once you have your design with measurements drawn out on your workorder or scrap paper (however you design) then proceed to draw it out on the back of the matboard.
I use my matcutter to draw out the outside lines. For instance, if you have any areas that have an outside of 3", then set your matcutter and draw that line on however many sides that have an opening that comes to that edge. Then you can measure in from those lines to create your openings and spaces between openings. If all goes as it should (and sometimes it really does!) then your measurements should come out correct on the opposite side of the board.
Another way to approach it is if I have any openings that need to be in the center of the board - I use a t-square to mark the center of the board and then measure out from that. For instance, if you have a 5x7 that needs to be dead center in the mat (and the board is too large to use your matcutter to mark it) measure out from your center lines 2 1/2 inches each direction for your 5" space and 3 1/2" out from the center lines for your 7" space.
In other words, you had to have drawn the design as you created it - just transfer this info to the back side of the mat JUST REMEMBER the back side of the mat will be opposite to the front when you cut it (mirror image) so be sure to place things where they need to be.
And of course, someone will say to just get a CMC and all your troubles will be over. But (in my opinion) you still need to know how to do it. Whatcha gonna do when the power goes out?