I’ve been sitting around the house just thinking about different cage options out there and I haven’t seen any screen cages for bearded dragons. Now I have a few ideas either because they’d rip them apart obviously if it was just bare screen cage, but let’s say someone took a 36x18x18 screen cage layed it on its side so it is now 3 feet long , 18 inches wide/tall. Lined the floor With cardboard then either tile , or linoleum. then the interior walls with the same cardboard/linoleum combo except for the front and ceiling obviously then mount the uvb inside on the back wall and the basking light from the top. This would give the cage plenty of ventilation but downfall from that would be it would be harder to keep an ambient temperature I’m assuming. Just brainstorming so any of you guys ideas and concerns are welcomed I obviously don’t have my dragon just yet but I’m just thinking of DIY cage options cause apparently the pre made ones suck and I don’t like the tank option I would rather have something Vivarium like permanently but I’ll probably just 20 gallon my baby at first till I either made something custom or bought something from someone but for the time being it’s at least fun to brainstorm and exchange ideas with others.
Screen cages are sometimes built to be used outdoors during the day. They are mostly for protection from predators in those cases. The reason you don't see too many screen tanks is that as you said, the ventilation is good but it's very tough to maintain temperatures. It might be less of an issue if your house is warm all the time. More popular DIY builds use a good quality plywood that will be somewhat lightweight but retain heat pretty well. I would plan on doing that and building it to dimensions of about 4'x2'x2' or larger if you have the space to do so.