GST REGISTRATION

good afternoon dear all CA Experts,
I am constructing two warehouse godowns, these are under constructing level. not completed. not ac godown. may be farmers/dealers will kept stock either agriculture produce or fertilizer or cotton lint bales etc in godown. in this regard first we have to take registration or not for godowns. if no registration leave it. if yes to take GST registration after constructing godown or under construction. please clarify