Congratulations Flyer on a great looking room! I'm a big fan of SMT room acoustics, and rate them in my top 3. Personally If I set up a dedicated, treated listening room, I plan on using a rough granite feature wall for my front wall (which will look cool, as well as provide diffusion), together with ASC room treatments, incl: their new Isothermal tube traps. Really great stuff.
The wings are available in MDF (with folio or veneer), acrylic or diy 10mm reinforced cardboard with raw mdf top and bottom parts.
Mine are in MDF (except for the transparent one of course). They must weigh about 10-15 kgs each. The sturdiness of the MDF ones (and hence their weight) is required to avoid resonance.