When building fuselage sides from sticks, the typical procedure is to build directly over the plan.  Protect your plan with a sheet of thin plastic.  My favorite plan protector is the backing sheet from Super Monokote.  I save the backing when I cover large wings, and I find that I can build several planes with them before they are used up.  Use pins to hold the parts in place over the plan.  When you finish, you will have a fairly accurate part.  The model shown in the photos below is the RCM Senior Telemaster.

It looks pretty accurate, but I’m sure there are a few errors here and there.  If the first side were removed from the building board and the second side built in its place, the errors in the right side may not match the errors in the left.  Also, in the case of this Telemaster, it’s easy enough to attach the braces to the inside of the right fuselage side, but attaching them to the left side would be difficult if it is built directly on the plan.

The solution is to build the left side on top of the right.  Remove the plan from the table and put it away, turn the right side over and lay it back down on the table.  Remember the sticks that were attached in the tail section?  There aren’t any at the nose of the plane, so we’ll have to shim the part with 3/8″ thick balsa blocks to make it flat.

There is no need to pin the fuselage side to the table.  Protect it with a plastic sheet.

Place the parts for the second side on top of the first.

Build the second fuselage side on top and pin it to the first side, to assure that the two sides are identical.

Now you have two matched sides.