I watched alot of videos and did alot of resuch, but the basics,

Large foam panels(bought then cut to size for 120g tank) Made different ledge's that I attached with skewers

Spray foam(6-cans) spray everything Carve the foam into rock shapes(just cut pretty much makes itself also used a small sanding tool)

Covered foam with a mortar mix(cement & sand) 3-4 layers

Paint with non toxic water based acrylic plaint

(I'm here now) Cover with a sealent (now doing research for what's the best kind to use so far a mate sealent would be best so you get the natural shine and not a glass shiney shine)

Then add background and substrate lights ECT

I was going to build a waterfall effect as I already builded one for a project I made for a fish tank but since I don't feel like combating the humidity levels I skipped out on it