You are correct in understand that "some" here means something along the lines of "about". In fact, I'm pretty sure this usage may have come from a phrase like "something along the lines of" or "something close to".
A "storey" is a measurement of building height. It usually refers to the number of floors a building has with smaller buildings. A good estimate is approximately 10 ft (3 meters) per storey, but it is my understanding that this is a very rough estimate and the "storey" is a rather vague unit of measurement. 90 stories makes for a very tall building, regardless of the specificity though.
Hope this helps :)
(One last minor thing: It's spelled grammar, not grammer ;) )