In many buildings, underground floors are referred to as lower levels. They are often abbreviated as LL1, LL2, LL3, LL4, etc.
Student or Learner
My office is in basement.There are four basemnets one after the other. My office is in second basemnet. Do I need to say "There is a four story basement. My office is in second basement"?
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.