Android 8.1 build procedure

[AlexS]

No one can give a small hint?
I did manage to build kernel within that tree. But i have no idea what mkimage.sh needs to work:

CROSS_COMPILE=/opt/gcc-linaro-7.3.1-2018.05-x86_64_aarch64-linux-gnu/bin/aarch64-linux-gnu- ARCH=arm64 ./mkimage.sh
TARGET_BOARD_PLATFORM=rk3328
TARGET_PRODUCT=rk3328_box
TARGET_HARDWARE=rk30board
TARGET_BUILD_VARIANT=userdebug
BOARD_SYSTEMIMAGE_PARTITION_SIZE=1610612736
BOARD_USE_SPARSE_SYSTEM_IMAGE=true
TARGET_BASE_PARAMETER_IMAGE==device/rockchip/common/baseparameter/baseparameter_fb720.img
system filesysystem is ext4
kernel image not fount![/data/store/eg/Rock64/rk3328v81_box/out/target/product/rk3328_box/kernel]
copy kernel from TARGET_PREBUILT_KERNEL[] (y/n) n to exit?y
cp: missing destination file operand after '/data/store/eg/Rock64/rk3328v81_box/out/target/product/rk3328_box/kernel'
Try 'cp --help' for more information.

I tried to set variable TARGET_PREBUILT_KERNEL to /data/store/eg/Rock64/rk3328v81_box/kernel/arch/arm64/boot/Image.gz but without success.

Can you just drop a small hint ? I'm not asking for user guide really..