If you have the time to share the details, I would definitely appreciate them (looking to do something like this myself). In particular, on which hardware did you build the kernel? Or did you cross-compile it? Also which bootloader did you use? Thanks in advance!
I built the initial kernel on an AMD 5800X running Debian - there are cross-compiling instructions on the Asahi Linux wiki.
For bootloader, I'm currently just appending the kernel & device tree to m1n1 (which is the first stage Asahi loader).
I suggest getting started with your rootfs and kernel under m1n1's hypervisor, as the virtualised serial ports make it much easier to debug initial issues.
edit: other than the install script which is linked elsewhere in this comment thread, everything you need is on the wiki in various places :)
