I've not looked in to new apps in years, I still have access to the old free version of inSSIDer but I've also used Wifi Analyzer from farproc (Android only I believe). Cannot vouch for the quality or safety of either at this point. Source: almost 3 years ago

You can also try our redesigned design.ui.com which will help you plan and compile your dream setup and suggest the necessary equipment for your dream setup to run as efficiently as possible. Source: 6 months ago

Ubiquiti has a tool to help with this. design.ui.com. Source: 11 months ago

Hi, u/carpau7000. We suggest you upload your floor plans to our Design Center and you'll see how many APs you'll need! Link to our Design Center – design.ui.com. Source: 12 months ago

You can always try design.ui.com you'll need to create (a free) account to use it. It's design for unifi products, but you can see how things work with their APs, and I'd bet you aren't looking at much better with other brands products. With your construction, you'll want to do everything as "outer walls". Source: 12 months ago

One on each floor at a minimum but why don't you play with it and your dementions here. Itis a good estimation tool. https://design.ui.com. Source: about 1 year ago