I've always wanted a mechanical keyboard with the layout of the Apple magic keyboard, couldn't get use to the windows key position and missed the fn key. Always thought about building my own
On an Apple keyboard the right edge of the X key aligns with the right edge of the command key, which makes it easily accessible by your left thumb from a resting position.
Most non-Apple keyboards use a layout where the command/alt key is half a key width to the left. It doesn't sound like a lot, but it makes those keyboards really uncomfortable for me to use.