I came home with a 4'x8' panel of quarter inch MDF, which the lumberyard had cut into 4 pieces. I didn't follow my own advice, which is to prime the each piece on both sides before you make your cuts.
No big deal.
I've gone with stock sizes, and common sizes for plein air painters. You can of course go bigger, which is an advantage with quarter inch rather than eighth inch thickness.
Here's a sample layout for a 2x4' panel.
The cut pieces were laid out on newspaper on my kitchen counter, which is handy for a lot of art things if you don't cook very often. I'll rephrase that. I'd much rather paint than cook.
As the cut panels were drying in my dish rack, I could attend to priming the edges.
At this point you can do your thing, which is to say, treat the panels for your medium of choice.
I went a step further, so one more blog to come.