Is your ceiling really 8 meters Above Finish Floor? That strikes me as odd for a room this size.
"...simplest way to make out estimate of..." estimate of what? Are you asking about legal occupant load for a room this size? Or, are you asking how much money this might cost, as in price estimate?
To calculate area one need not specialized in Civil Engineering. Middle level school mathematical training is enough. I presume he needs cost estimates along with Bill of quantities.
"Almost" Good Answers: