Hello; My advice would be the Sig Mid-star 40; good instructions, good wood, an easy build, and it makes a terrific plane. It's my favorite 40 sized plane. The next choice would be the Sig four star 60, another easy build with interlocking parts. But you did say 40 size. I have built most of the Sig line, and except for a few of the earlier ones, there isn't a bad one. I have also built all the Goldberg planes too, they're all good too, and they make a good flying plane. I would say that you can't go wrong with either of these makers.