If you want to build light weight you have to look at every detail.
Starting with the "frame", pay attention to Andrews minimal frame.
It is hard to beat 1/8 lauan or baltic birch for weight/strength.
If the Pico is too small look at the UltraLight or the Superlegra, but keep it simple and watch every detail.
In the end, however, unless you are pulling it with a very small engined rig, much of that search for the ultimate light weight is a waste of time.
Sorry it is that way, but we did not invent physics.
dave