Open-frame is cheaper, anyone can build a open-frame; it easily be assembled with PVC or wood using the width x length of the motherboard. The PSU can be below it, illustrating a type of oil rig structure conception.
Enclosed-frame can be crafted with wood, with an opening on the side of it just big enough for the intake wall-fan/filter, a door big enough for troubleshooting, and slits for the GPUs. Inside and under the GPU slits are cheap aluminum shelve mounts or 2x4s that allow the GPU risers to rest/mount. 2 or 3 more custom mounts for the PSU and the motherboard to operate. Any blower type GPU would be idle for this build. Also, an exhaust fan would mount above the intake wall fan or direct the hot air inside the house, building, fish tank, etc.