Well, you can certainly build up the wings, and put most of the fuselage together.

Eventually, you will need servos, a motor, motor mount, fuel tank, and a receiver. Most kits come with most of the items, some include a tank, but some don't.

You can certainly build just about everything without having most of the additional items needed for flight. Servos, for instance, can be mounted just about any time because of where they go. I had a Four Star 40 but can't remember if it already utilized two servos for the ailerons or if I added them myself. Some come with one servo in the center with torque arms going the ailerons on each side. If the out of the box design comes with one servo, in the center, then you can put this on just about any time. If you decide to do the dual-aileron servo setup, you will have to decide when building the wing and not include the torque rods and make the servo mounts in the center of each wing side, centered on the middle of the aileron for that side, and against a rib or hard point. You can build in a hard point for this at the proper rib (center rib) for the "servo box" during the build process using 1/8 ply.. and, as I said, I don't recall if the Four Star was already dual aileron setup or if I added that myself. If you do decide, as I said, you have to make that decision before building the wing.

As far as the motor is concerned, well, you can certainly build everything without the motor and motor mount, then when you get the money to pay for a motor and mount, you can add those at that time.

I don't really see any roadblocks to building without some of the "required" materials.

Of course, you will need glue..

CGr