it's possible, but a lot of works involved esp in the curing part.
if u had the patient & things to start, then u could end up with liverocks which is molded to your liking.
u had any idea where u can get portland cement?
just make sure u dun go into those contractor shops selling such concept, esp alantis something...u will regret big time.
it's better to diy on your own design.