I'm not sure which kit of the model you have but... Brodak kit this airframe and have a Instruction book for the build.  It is available as a stand-alone item that  may be something of a guide if you like.

http://brodak.com/59-ares-instruction-book.html

There are many mentions of the I-beam wing construction here on the site, just use the search engine at the top left corner.  I looked for a build thread but did not put much time or effort into it.

Here another link related to an I-beam build.


http://stunthanger.com/smf/classic-planes/my-first-'i'-beam/

Bob Hunt (Robin's View) has an excellent video available which shows the construction of the wing by the designer himself. It is a build from plan demonstration but will answer all your I-beam questions I'm pretty sure.

Ok I cant stay away from the elephant in the room,, .
If this is your first control line plane,, some helpfull advice perhaps
I admire your shutzpa to build an Ares, actually the build will probably be fine for you, though there are some unique differencew between RC and Control line,, ( examples, Hinging, covering, weight, and trim)
that said,
Please do yourself a favor and research on here for beginner setups,, something like a flite streak with an LA 25, or a Skyray

I am concerned that if you fly this plane as your first endevour, your will meet with displeasure, not because the airplane is hard to fly, but more the guy on the handle and the learning curve there in,, with a less complex model, more easily repaired, less time invested in building, WHEN you smack the ground, and you will,, you will suffer less frustration and loss off effort if you start off with something simple.

Please do yourself a favor and research on here for beginner setups,, something like a flite streak with an LA 25, or a Skyray

Some people need to discover this for themselves.  For instance, I have a blue box Nobler hanging in my shop that'll never fly again -- it was my first "big" CL plane, and my opportunity to realize why you want to start out on something easy to repair.

Crash for crash, there are "events" that a profile will survive with minimal damage that would leave you picking up an Ares with a broom.

You risk having your threshold of what you consider "good" to rise beyond what you built into the plane.  That's part of the reason that Nobler is still hanging on my wall.  (And I was in about the same position as you -- I had decades of building RC planes and some casual CL behind me, then I built the Nobler from the kit).

BUT -- if you just want to build it, go build it.