I am looking to build a resort from scratch in Roaring Heights from an empty lot. How do I do that though? Like what do I need to build one, and how do I set it up. I know already how to manage one. I need to know how to build one, and how to set it up.

If you want to do it to have your sim as a resort owner, you just need to make sure there's a big enough lot to use that you can afford, use the computer (under the real estate section, i think) to select become a resort owner or something along those lines. Once you do that, the front desk will be placed on the lot for you like a mailbox on any home lot. Build a room around it to be your lobby (i usually add bathrooms and a sitting area, plus decorations for stars). After that you just need one tower to get started, and those will be under the "improve resort" tab just like when you're managing one. From there, build a dining area etc, everything else as if you were starting at hobarts hideaway. A note, I don't play roaring heights, but I've been told resorts do better when they're on the water/beach so if that applies, take advantage of it I guess.
If you don't want your sim to be a resort owner, and you just kind of want to build the five star resort independently for your sims to enjoy, in edit town you can change any empty lot to a resort lot and the rest of my advice holds true, front desk magically appearing and all. There is also an excellent guide to it on carlssims3guide, how to build a five star resort from the ground up Sorry if this wasn't helpful at all. I've built them from the ground up but I'm not the best at explaining things.