This situation they give only the floor area of the building and they want the approximate electrical load for the future purposes. Is their anyone here willing to give their ideas or formula to compute the load as easy way. Including the mechanical load.

Why are you asking for this info? Are you an engineer?
What kind of occupancy? Business, Mercantile, etc..
What is your general location?

What you are asking for is actually a useless piece of information because it is not in context with the entire load you would need for a building.

There are formulas to calculate elements of the minimum levels of electrical service based on the sq. footage of a building.

However as with the previous answer the calculations are based on the type of building (residence/commercial/industrial/theater) and so on.

BUT this will only give you the general use range of service and is woefully inadequate.

For example ONLY: 3 VA * Outside building area for a residence will give you the general use and lighting load only. No load calc for heating/AC washer/dryer or other required loads.

In a commercial environment that same information would give you only the lighting and none of the expected load for signs, receptacles, motors or heat.

A full "Calculated Load" study needs to be completed