If you have decided to build a rig with 8 GPU’s then you will be able to find several motherboards in the Rig Builder to choose from.
All the boards that say they accept 8 GPUs in the builder are based off the Z270 motherboard architecture and have only 6 PCIE lanes but with an adapter you can use the M.2 ports on the motherboard with M.2 PCIE 4X adapters like the one below to hook up your 7th and 8th GPUs
These adapters are easy to find on eBay and only cost a few dollars, just do a search for “M.2 PCIE 4X” and you will find lots of options. This article from Nice hash details how they made this 8 GPU Rig:
YouTuber Cryptomind also shows you step by step how to set up a Asus Z270-P motherboard with 8 GPU’s in this video:
That should be enough info to get you assembled.
Now the last part of the puzzle is the BIOS settings for the motherboard and getting the OS to see all of the GPU’s, I have seen many users on the forums that have problems with windows 10 recognizing their # of GPU’s (4-8) and I have found this video that has a very good step-by-step process to setting up your motherboard.
That’s all for now, happy Zcash mining!