Is there anybody out there with expertise on buildings that can tell me what the lifespan of a well maintained apartment building would be? I guess a lot depends on the original quality of the build of course, but lets assume a pretty decent one.

On record, the oldest is about 30 years and still going strong. Needs elevators to be replaced, and within the next 10 years, water pipe systems as well.

I live in a block in Pattaya which is over 30 years old and is in excellent condition. Don't think that these newer ones will last that long!

Siam Condo opposite Fortune Town is 30+ now and it looks it too, not about to fall down for another 20+ years though

Impossible to say, building quality and especially maintenance decides.