No material restrictions. Most are building with as much carbon fiber as they can to keep them light. To light wouldn't be good either though in my opinion. Most are going with the widebody tall fuses as they perform fai schedules better. Also 4 blade props are becoming very popular now. They give a constant flight speed in all lines.. Fixed gear has become the norm, not that I have any. And there are no height restrictions for how tall you could build the plane. There is a sound restriction of 98 db. And electric pattern ships are starting to do well.

Krishlan