You can do DIY mold forms using sand as a base and plastic sheeting or silicone in a box. This is most often going to be for precast stuff you mortar onto a fl

You can do DIY mold forms using sand as a base and plastic sheeting or silicone in a box. This is most often going to be for precast stuff you mortar onto a flat surface elsewhere but you can create some very fun curved surfaces in place as well. As for other materials, I love wood but concrete wins for water/fire resistance and metal is expensive.