Newbie. Question about sealing a room

Hi everyone. (I have read through the rules and I hope I can abide by them.) Great site! I have enjoyed reading through all the posts. I have recently blocked in where my garage door was and installed a sealed double glazed unit. I intend to build a home mix room for my portable Protools rig in this new room and have found some detail drawings on the sae site that I now realise are the work of John Sayers. The garage has a flat roof and one side adjoins the outside wall of my house. I want to be sure that I can work late and not have my young children complain about the noise. All fairly standard so far I know. I do however have a twist to all this....... I want the studio to look like a standard room and also be used as a spare room. I am putting a nice sofa bed in, to double for client comfort and spare bed. I have been intending to build a fairly standard 'inside out wall' type construction. Whilst talking to the building inspector who is overseeing the construction I realised that I had overlooked something in my plans. Because I want it to look like a standard room (and because the building inspector requires the window to be a fire exit) I haven't intended to put a pane of glass in the inner room. I had purely intended to take the material surface of my finish across onto the sill of the outer window. I have realised of coarse that this will destroy the seal within the room. I am wondering now whether I can achieve a seal to the window in a similar way to the floor. ie. a window board and surround (maybe mdf or suchlike,) mounted and sealed against neoprene. The building inspector also raised a concern that with all the Rockwool/Fibreglass I intend to use there will be a danger of condensation because of the un-vented airspace in the ceiling cavity. I have to admit I was a bit confused by this. Can anyone help answer either of these questions? PS. The wall that has just been built in the front of the garage has two low-level airbricks to vent the timber floor. Is this a problem? Thanks in advance to anyone who has read this far....

Dan, any chance of a couple of pix and/or a floor plan so we can get a better idea of what you have? Thanks.. steve

Very Basic I'm affraid but hopefully these will help.

I have also taken these pictures showing the window, which is yet to be installed and also the ceiling. I have been doing some research into the condensation question. What I understand is that due to a lack of air circulation there may be a condensation problem. The building inspector suggested putting four mushroom vents in the roof, although he pointed out that this would spoil the insulation rating and therefore require a further 10 inches of rockwool. I can't say I'm keen to put four holes in a flat roof as they are notorious for leaking. Is this my only option or can you suggest another way? Thanks for the response Steve.

Sorry. Should have resized the hieght, not the width. Here it is again.