That was pretty much my plan as well, to build a frame though I was thinking a bit more along the lines of using angel ( was thinking 2 inch angle, 1/4" stock) dropping 1/8" pvc sheets into each "window frame" but the cost of the aluminum and the extra work required seemed like over kill.
My worry about sliding doors has always been the track,most track is rather sharp and while I don't plan on dragging a snake out of it's enclosure I would like to remove any possible sharp area my snakes or anything else I decide to hold in an enclosure could accidentally catch itself on.
So it was in hopes trading a afternoon of sweat and work in the shop to get what was essentially a T-8 or T-10 ( not sure which I would want to order just yet, the extra height seems like it would be nice) about 100.00 bucks cheaper. That 100.00 is money I could put towards the next enclosure or future snakes or just about anything related to the hobby you know.