dear niladir mukherjee,

if you wish to estimate repairing works in a school building first of all you need to verify which items need to be repaired.

before estimation you need to check a few items in a building such as age of the building, structural cracks in beams,columns, walls etc., concrete spalling areas, appearance of a building such as painting, ceiling etc., and electricity supply,water supply,fire services, lift and escalators, air conditioning / heating system of a building.

after checking you need to decide which works in a building to be repaired.

finally depends upon requirement prepare an estimate.