I've tried using it over the years but I never liked it because there was no information. So last night I looked at my local city and there is almost no information at all. I spent a few hours last night adding buildings and restaurants and removing incorrect items. It was actually kind of fun and therapeutic and I plan to do more of it tonight. My girlfriend thinks it's dumb and I'm wasting my time because Google maps and Apple maps and Bing maps exists but she just doesn't understand open source.
Edit: Apologies, I just realized this question is not Linux specific.
Probably the best way to contribute buildings is using the JOSM editor and the buildings plug-in.
It's only available on the computer and it has quite the learning curve, but it's a very powerful tool for serious editing. Usually the iD editor is good enough for easier editing than on mobile.