After reading the discussion thread down below about Vega cylinder-back mandolins I searched the web for photos and descriptions of these instruments, as I've never encountered one. The design intrigues me and I'm considering building one.
I'm curious about the top bracing. I would guess that the tops are ladder-braced since most bent-top mandolins and guitars (such as Selmers) have such bracing. I'm guessing that there is a brace under the bridge, one just below the soundhole, and a third between the bridge and the tailblock.
Though one repairman is on record saying that the back is carved, and Rigel does this on their reproductions, I think it would be feasible to press a flat plate (using heat and moisture) over a form to create the cylindrical back.