How do you ask a question?

I am sorry if I am asking this question in the wrong place. I've tried to find the answer on my own..... Sims 4....City Living....I am seeing speed builds on youtube where people are building penthouses....how can I do this? Where do I go to start? I've gone into manage worlds, but when I click on an apartment building, it doesn't give me the option to build a penthouse, it only shows what apartments are available. WHAT buildings can they be built on, and how do I do I get started?

Thanks,
Tonya S