In addition to code, I think 0-indexing is also a nice convention for floor numbering. That way the Nth floor is N floors up from the ground level. This is already how basement levels work.
0-based floor numbering is infuriating. Telling someone that you live on the third floor which is actually numbered 2 is honestly dumb. I had to emigrate from the 1-based floor country a year ago and first floor numbered 0 is still throwing me off sometimes. And every single time I want to raise attention to a window somewhere.
If we admit negative numbers for basements, then were are not using the natural numbers anymore. This is a completely different question since the integers does not have a beginning.
This is not a 6-hour slow risposte; it's my 6 hour anti procrastinate filter I swear. Anyway, just like all animals of habit, I immediately I agreed with floor zero because I come from a place where the lowest floor is not floor 1 (unlike the US). However, I can see somebody saying floor is the height of the ceiling, so floor 1 = 10 feet; floor 0 (underground) 0 feet. One thing we can all agree is that the calendar, without a zero, it's pretty bad.