The Google / Skywater shuttle reserves about 10 square mm (10 million square microns) of space for your design.
This comparison that Mohamed from efabless put together shows the various areas (and time to generate the GDS2 files) of some popular designs.
We could fit in about 10 picorv32 RISCV cores!
I currently have 3 designs ready to add to the multi project harness:
There is a lot of room for simple designs!
Final ASIC application
You can see the final application here, we fit in 8 designs with room for more.