Not handy now but their pretty basic. I just angled them 45-90-45 kind of like this following poor ASCII illustration _/\_ then screwed the flat surfaces to the walls with the cables inside. Like "A"s with feet. But my sheet metal bender (whatever their called) can't take wider peices than 2 feet so I got shitloads of seams
. Quick fix not the pretties, looks kind of industrial. Although the plans for my new furniture looks industrial as well and I have no budget for them ATM but they would make most of the covers obsolete. And yeah the plastic covers would have to be checked daily if your bird have any interest in them. If your confiteble putting new connectors to your cables you could always use steel tubing without having to have a massive diameter. Lots of work tho, but removes fabrication times for other solutions. Making covers out of wood should work too, but they would take more space and also like plastic ones they may need frequent maintainance. I do however bet that a lot of the bird proofing here is too much if I never had a bird out unsupervised. But I leave one out sometimes while in the workshop doing something or in the studio painting. And I want no accidents to be possible while I'm out.
An example is landIng ontop of a tv or screen since they can get their toes stuck in the ventilation slits. While some risks can be eliminated, some minimized others will always be there, even for a caged bird. All we can do is our best, so my option. I live in a huge birdcage and adapt my items to not cause any risk to my winged friends...