Provided a minimum time,how best do i quickly achieve a freehand sketch of an existing building with multiple interior spaces & funny exterior shape?

Look before anything you must know that all of humankind are born with same skills but talent matters after all so , you should practice daily for minimum30 min and then you will got the ability to draw whatever you ever want in few minutes.   

It is a talent, however if you start practicing daily for at least two months you will be able to draw a sketch within10 minutes regardless how difficult and detailed it is.