" I would like to model my school as FPS war game."
Your school/head of school might not like this (And can even ban you from your school) as its basically a school shooting. You can understand why this is an issue right? (In theory it could be used to “Practice” a real school shooting).
But to answer your questions, 1 unit in 3dsmax/maya is 1 cm. so 71 meter is 71x100 is 7100 units.