How to build the official docker image of alpine linux?

I would like to know how to build exactly the same image as the official one ?
When I use the alpine-make-rootfs script, it doesn’t give me the same hash as the official alpine-minirootfs-3.14.0-x86_64.tar.gz
I tried different options with the script, but the hash is always different.
Official (3.14) sha512:
d90ddc3346c1ee1dc3de17fa8b03a3450fa08e8ceda73be2fadab2de55db232cffffab227b7eaa61f11f54f515232d01bd495a302dd5c70bb5ed8f1b7e30325e

My rootfs (3.14) sha512:
1e9f3551cfaafecb3d213d91b4e1be1a928c19b87c49bb6329fc1989677e95e4acb7f794879bbe153e9243d009ccddc654bb4c48389d6b7a8cc38ebb066e740d

I used this command:
sudo ./alpine-make-rootfs --branch v3.14 --timezone 'Europe/Prague' --packages 'openssl-dev' --script-chroot rootfs.tar.gz

how do we do it for other architectures? via qemu ?