I need someone to help me build a minecraft world

I need a 3 section world one section with a giant tree fairy style then one that has a giant mountain in the middle with huge connected caves on the inside and the last one is a gigantic floating island with roman/forest like structures. I want walls separating the three sections and outside the walls of each section I want a forest. I'm going to use it for lore so I want it to be detailed and well built, thanks. I will help in any way I can I just need expert to help.