I designed a few shelves for below my monitor with roller shutters and I integrated two USB-hubs. As mentioned in some comments, the whole thing is a little bit challenging to print and to be honest the roller shutters open and close just fine, but are not as smooth, as I expected. Nevertheless, I'm really happy with it and just wanted to share it with you. So here are some more infos.

Everything is printed with Prusament PLA Galaxy black a nozzle diameter of 0.4 mm and a Layer height of 0.15 mm on my Prusa MK4 printer. (DokterWagemaker@Moritz_988877 commented some stringing with PETG, so I recommend to use PLA.)

The design mainly consists of 5 parts:

1. The left shelf
2. An angle piece with an opening for an usb-hub
3. The middle part with a hanging shelf (with a cutout for the monitor arm) and a small cover below the shelf (for the monitor stand). This cover has a small whole for my remote control.
4. Another angle piece with an opening for an usb-hub
5. The right shelf

All the shelves can be also used separately as well, so you don't have to print he whole thing! 

It was designed for my monitor (Dell S3422DWG) with the original stand. If you want to print the whole thing and put it under your monitor, make sure you have the same or a smaller stand! The overall printing time was a few days; the amount of filament was over 2 kg.

The angle parts have openings for threaded inserts (M3*5*5) and I fixated all the parts with some M3*8 screws. As mentioned the shelf in the middle is hanging, so here you need to fixate the shelf at the angles (you could probably also use some glue, but I recommend the threaded inserts and screws).

The right and left shelf (part 1 and 5) are printed lying on the outer back side of the shelf. The rails for the roller shutter need support! For the roller shutter I used 16 middle parts and printed them lying on one of the long sides, because they are too long to be printed upwards. Also here you need support and it can be a little bit challenging to get the support separated again. (Maybe some organic support would be better here. If you try that, please comment for the others). The stopper lies just under the roller shutter and looks nice.

The angles (part 2 and 4) are also printed on the back side (see picture) and with support. As USB-hubs I used “Anker Ultra Slim 4-Port USB 3.0 Data Hub”. I had to remove the plastic of the USB-plug and saw a triangular piece (from the blue light to close to the cable start) of the hub cover to fit it in the angle piece. If you want to do it, plug it out, don't cut yourself, and be aware that the warranty is gone!!!

The middle shelf (part 3) was the one I updated first. It has this weird cutout in the back for the monitor arm. This was also printed lying on the outer back side. Here I recommend to print the middle parts of the roller shutter (I printed 11) standing on the closed end (see picture), because so you can print it with minimal support. The cover for the monitor stand was printed lying on the front side and with support.