Experts Exchange - Need a Clue Corel X4 Solution

This is a potential solution to this question: www.experts-exchange.com I imported a TIF drawing of a small storage building. It shows SOME dimensions of the building. I want to be able to use the Dimension Tool in CorelDraw to figure the sizes of ALL objects in the building. How do I synchronize ONE dimension to my ruler scale? For instance a door is exactly 36" wide and shown. How do I resize the item so that if I draw a line the same width as the door it will show me 36 inches, mm, cm or whatever? Many dimensions are not shown so I must use CorelDraw to tell me with the dimension tool the exact dimensions of items lacking them. Any clues for me to try out? I am an EXTREME NOVICE at CorelDraw, but I know it can be done.