How can I add a 3-D effect to a building facade.

Having drawn a fair number of presentations using that old stuff like pencils and pens I would say adding shade and shadow to the window and door openings and under any eaves or overhangs is the easiest way to fake 3D.
The architectural convention is to assume the sun is located in the upper left corner and casts light at 45 degrees.
Hi.

oh i understand your question now