I designed from scratch these modular shelves which use 8 mm aluminum round tubes as structure. These tubes are very cheap and can be found everywhere, the price is about 1.5 € per meter, so it is unexpensive (you won't need more than two meters unless you make very very large shelves :D).
I included straight and corners variants so you can virtually made any design. I designed it to be screwless wall mounted, since I used it in bathroom and I didn't want to damage tiles. You can use any powerful double side tape. You can also use command strips which have proven strength (there are waterproof command strips to even mount it in shower). I also added brackets for corner and end sides to increase the wall fixation if needed, they are mounted below every part, although I didn't need them.
All you need to do is to print desired bases (printing orientation is shown in images, supports are not needed for any part), ends and corner (this last one if you want to mount the shelve in a corner as the main picture, but you can make it only straight). I included the tube lenght inserted into every part in three pictures. When prints are finished, you only have to cut the total tube length adding these distances to the tube (they don't need to be exact at all, it is better to have shorter distances to avoid any separation in bases).
Parts named as hollowed have a little cut-out to allow any wire to be inserted. Note that I've enlarged this cut since I notice they were too short, now it should be working properly.
I highly recommend a tube cutter like the one shown in picture because it makes clean cuts (8 bucks or cheaper in any hardware store), but you can use whatever you have (dremel, hacksaw, etc...).
Finally, you have to assemble the structure as seen in photos (in case tubes are too loosed, you can use a hot glue drop to fix it) and then press the bases until they are introduced in rails.
There are several parts with different dimensions and orientations, but you can also scale the bases only in the same direction as staples to virtually make any needed dimension (if you scale other directions you will deform the staple which is inserted in tubes).
It is a very easy project, hope this is useful for you guys!
Feel free to leave any comment or doubt!
These are very easy prints, although they're large. It is important the resolution only for holes, since I have printed them without supports. It will depend on your bridging bahavior, but you can use supports for holes iif you prefer to get a perfect circle.