I work with pulled sugar and isomalt frequently so just a few thoughts for anyone looking to purchase one of these warming boxes. Understand that these are just my observations after working with boxes made from Plexiglas and those made from Lexan.
If your going to purchase one of these or make your own, PLEASE stick with one made of Lexan. While Plexiglass is cheaper, it will have some issues from the high heat it will be subjected to if you work with pulled sugar or isomalt on a regular basis.
Lexan is is a polycarbonate sheet of plastic. It is durable, extremely heat resistant and is so impact resistant that some varieties of "bulletproof" glass are made from it. This means that after repeated long exposures to high heat (such as a warming lamp), it will retain it's impact resistant qualities and will not shatter if subjected to impacts such as dropping it or smacking it accidentally with tools in your work area.
Plexiglas is not a polycarbonate. It is made of acrylic. Plexiglas is scratch resistant as opposed to impact resistant. What I have found, while working with Plexiglas, is that after long periods of being subjected to high heat, it will tend to become more brittle. What this means is that your Plexiglas box will tend to have a higher chance of breaking, cracking or even shattering if dropped or impacted with a tool in your work area.
If you plan on working with a warming box for awhile, the Lexan will stand up to anything you can throw at it and it will have a longer working life than Plexiglas.
Another consideration on these boxes that they're offering is that they do not come with a face shield. On my box, I have a wooden face shield mounted at the top front of the box that extends down about 9 inches. Again, if you plan on working in front of this box for awhile, the heat from the lamp is going to be a bit much without something to block that heat from hitting you right in the face. It also helps to cut down on the heat lamp glare that will be shining into your face constantly.
The face shield protects your face from the heat but you can still see what your working on and allows you more time to comfortably work.
Again, just my observations and personal thoughts on the subject. I love working with pulled sugar and isomalt (especially isomalt) but I love it even more when I know that my equipment is going to last for a long time and I don't have a heat lamp trying to fry my retinas