I'm not a "recognised dev" and honestly I'm only a bit better than a noob but usually to create a flashable rom i do this things:
1)i customize my rom and i flash the kernel i want..
2)i do a nandroid backup, i extract the /system folder which is ".tar" using "zArchive" (I'm not sure about the name you can search on play store "tar opener")
3)i "steal" a meta-inf folder from other rom and finally i create a zip file with a)boot.img; b)meta-inf; c)system.
To do this i don't need to switch my computer on!!