That'll be fun! I designed and had built an aviary when I was a lot younger. Lots and lots of drawings
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My garage is a single, however I have mostly clad and insulated it now. When I moved in the back half was a rubbish shiplap single skin wood construction with an interior glass door, whereas the rest was brick, and the usual bent rubbish up-and-over monstrosity at the front that had one spring off.
First I had an electric roller garage door fitted, then took down the rear wall and re-built properly after laying a nice foundation in place of the crumbling stuff there previously. Wall was timber frame and then a proper steel secure door thing, widest I could get. Worked great for the K but the flipping GS is just that bit wider! I now have to take the hand guards & bar ends off, and still scuff the engine bars on the door frame! (This is because I like to clean the bike in private :/).
Last year I did all the insulating, cladding, and also sealing the bottom couple of courses thanks to next door's extension throwing water at it. I've now got the back half as my beer storage and serving area (home brewing remember, so a freezer that works as a beer chiller). I also carpeted it (threw down old carpet from the living room, as Brian can attest!) and put a rail up to hand my bike stuff. Lid and boots also live there now.
Winter time it started getting pretty humid so it now has a dehumidifier that I keep meaning to hard-wire an exit spout to. Anyway now it's lovely. Beer in back, bike in front. Just enough room to do stuff... but i'm still having a double next time!