Be careful which BS you believe and which you propagate. Bangkok, while generally flat, does have some local variation in height up to +/- 3M. Some areas will be fine and some will be deluged. And some poorer areas completely away from tourists might be flooded for a long time but in general the main parts of the city are built on higher ground because that's what you seek out when building in a swamp (think the French Quarter in NOLA).

There are maps showing the variation in elevation, in a generalized way, of districts of Bangkok. I haven't seen any in English, and don't have time at the moment to search for any, but I'll try and find something to post later.