What should I do to make an application?

"I don't think it's in foreign countries, so I'm going to make it."

Google any country name in English and write "rent" next to it. It's just something you haven't looked for and it's already there.To tell you about Australia, where I lived for a while:

They're all actually very important information sites.

"How to get information on rental buildings in each country"

It depends on each site-specific concept and on the real estate regulations in each country.

Is it possible if I take the information from the overseas real estate website and put it in the application? ... Do I have to give a settlement money or something? I wonder how much I should give if I give it to you.

You think it's too easy. If you've read it twice above, you may have a rough idea, but there's no way to know who owns this information and how far each person in charge wants to disclose it. Above all, this is about overseas real estate sales, and it seems urgent to review whether such information can be collected and uploaded.
There are two main optimistic scenarios.

To sum up... If you want to make an application like that... Don't just make it.