Norbe,
Connect the wings with the wing tube but not on the body. Then you can measure the wing tip and with a string stretch it tip to tip and transfer that mark to the wing root. Most find it comes out at the front of the wing tube or 6 inches in from the leading edge.

Also, there are two good sized threads on this plane already. You'll get more opinions and advice if you ask questions in those threads (although not as good as mine ).