If your plan is like my Kadet Jr, it actually shows a wing rib shape that you can use to make the appropriate ribs from. Since the wing is straight, without any tapering, all the ribs are the same EXCEPT where the spar is doubled. Shouldn't be a real issue to make the required ribs, as long as the plans have the profile on them. As far as the wingtip, just cut a rectangle that is over-sized and sand it to the final shape, other than the bottom bevel where it is glued to the outboard rib, after it's installed. Conversely, you could take a piece of balsa block and shape wingtips in the shape that you desire and glue them to the wing tip rib after you complete the wing build up. Either way, since you downloaded the instructions, it's not a complicated build if you follow the instructions.