"height" isn't a command, so it wouldn't work.
In this sort of circumstance you should
always check the command ref, to see what it can tell you.
I can't remember the easiest way to do what you are trying to do ... and it depends whether you want height above the ground or above sea level. The basic principle is to set a game logic or trigger at the relevant place and measure the difference in y coordinate between the two. (OFP calls height the y coordinate - it goes [x,z,y])
I have a feeling that triggers are always at sea level, and GLs are at ground level, but don't quote me. Search the forum, this has come up before.