inner leaf for live and control room...........

salam , this is the extended question from the thread "small studio in Dhaka"...as the last question is not responded i thought may be its because its related with this section of the forum......... @ Soundman2020: as my outer leaf of the studs of the sidewall is done ,i really need to be clarified one thing..... should i use 18mm plywood or drywall(12mm available)....or aboth at inside leaft both the room?...i bought both.....if it is ply should i varnish them or what type of polish for less reflective(as one of my friend used veneer board and colored... which later caused bad reflective sounds at mics) ?......i mean mostly at drums room? the ceiling is done as u told me ......insulation(hanging)..+ dual drywall + stud padding with glasswool (30-45 kg density which i found later) +drywall(new inner ceiling).....im attaching current progress pics .... the original post and plan layouts.... http://www.johnlsayers.com/phpBB2/viewtopic.php?f=1&t=17385 now all the work is hanging on this decisions.......