I'm not a rack designer, and I salute your idea, because it looks OK and is probably gonna work at least a bit, but I would be very careful with two things:
As you add servers (weight) to it, the base support will likely collapse.
As you add servers, the sides might "skew" and eventually make the whole assembly wobbly/unsafe. Normally, racks are either welded solid, or rely on transversal, lateral, and diagonal reinforcements.
Thanks, I will test it full of cinderblocks before putting in my server. Might add plywood or osb panels to the side if it need further reinforcements.
Panels on the side, especially if screwed/bolted, are going to be pretty good for stability and overall robustness. An alternative to that would be metal braces, corners, etc. Specifically cross bracing.
I would suggest to look at existing designs for how to reinforce the angles. Also, there caveats specific to wood designs (wood fibres direction, proportions, shapes, wood type, quality, density, etc). You might want to ask on a woodworking specific forum.