It's a low profile GPU, so I've marked that as 8CM (6.2cm for the card, the rest for motherboard headers and additional misc space).
As for the lower chamber, a SFX PSU is 5.1CM tall, so I gave it 6CM for rubber spaces below the PSU.
But I did consider making it a full height GPU, therefore...
This place has become a dump for ITX ideas so here is mine. I would personally love to have a case like this, a smaller prodigy with ample space.
22x22x14 Version (LP GPUs)
22x22x22 Version (TALL ITX GPUs)
Just throwing a thought in seeing as so many people are right now.