The only type of small form factor pcs that are worth building are the steam box types with the pciexpress angle adapter.
The ATX/micro-ATX/mini-ITX standard makes me frustrated. The slim mini-ITX cases have the air-intake for the CPU on one side and the intake for the GPU on the other. I wish the GPUs had the components on the other side!
The alternative to riser-cards would be to use a long riser-cable, but sooo long and susceptible to electrical interference.
Cube cases with horizontal motherboards are ridiculous. I hate them.
It is such a shame that nobody makes BTX motherboards any more. Some high-end workstations have motherboards based on the same principles, but those are custom-made.
I wish PC motherboards were made so that it would be easier to build something resembling a vertical thermal core, similar to the Apple "ash-tray" Mac Pro.