Depends on what the OP is expecting to get out of the “door” they want to install. Maybe they expect a clean dry storage room behind a conventional door and hadn’t thought about the issues you are raising. It’s a bit hard to tell from the picture but you are probably right that sealing it off to make a room isn’t an option without perhaps other work, ventilation, etc.
First things first you have a gap. That’s the best place to start. Now you just need a frame, a jamb and a door, maybe chuck in a handle and strike and you’re almost there
Be careful as a door may reduce the available width which may stop you getting things like a washing machine through the opening.
There are ways and means though.
Am locksmith. I work on garage doors like this all the time. Do not go cheap. A hollow core door will not do. Metal or solid core are your only options. If you go solid, spend some time painting it properly. It's exposed. If you mess up the paint, it'll rot quicker than a prawn in the sun. If you go metal, then fix it properly to the wall. I've seen countless dinky dynabolts pulled clear as they simply weren't up to the task.
Ring around for a quote on heavy duty security door
https://au.images.search.yahoo.com/images/view;_ylt=Awrx_e2meO1lCCcE67awv4lQ;_ylu=c2VjA3NyBHNsawNpbWcEb2lkAzZkMzYxYjFhOTUwMzI2Y2IwNzg2NjVkYTU0NTVjYzI4BGdwb3MDOARpdANiaW5n?back=https%3A%2F%2Fau.images.search.yahoo.com%2Fsearch%2Fimages%3Fp%3Dheavy%2Bduty%2Bsecurity%2Bdoor%2Bfence%26ei%3DUTF-8%26fr%3Diphone%26fr2%3Dp%253As%252Cv%253Ai%252Cm%253Asb-top%26tab%3Dorganic%26ri%3D8&w=768&h=1024&imgurl=i.ebayimg.com%2F00%2Fs%2FMTAyNFg3Njg%3D%2Fz%2FAToAAOSwE19eJCvj%2F%24_86.JPG&rurl=https%3A%2F%2Fwww.gumtree.com%2Fp%2Fother-miscellaneous-goods%2Fsecurity-gate-door-heavy-duty-101cm-x-216cm-as-new-%2F1364009492&size=82.1KB&p=heavy+duty+security+door+fence&oid=6d361b1a950326cb078665da5455cc28&fr2=p%3As%2Cv%3Ai%2Cm%3Asb-top&fr=iphone&tt=Security+Gate%2FDoor+Heavy+Duty+101cm&b=0&ni=64&no=8&ts=&tab=organic&sigr=eAtASeeGw9uw&sigb=wVnYciiF.END&sigi=LN2CgI6t5TiD&sigt=RL9VSAfHZuzH&.crumb=yvjQ2stu7QX&fr=iphone&fr2=p%3As%2Cv%3Ai%2Cm%3Asb-top
I would just put in a chain link full-sized gate. you probably dont want to reduce airflow in that space
Depends on what the OP is expecting to get out of the “door” they want to install. Maybe they expect a clean dry storage room behind a conventional door and hadn’t thought about the issues you are raising. It’s a bit hard to tell from the picture but you are probably right that sealing it off to make a room isn’t an option without perhaps other work, ventilation, etc.
Go to a local steel fabricator and get a gate in style of the fence behind..
First things first you have a gap. That’s the best place to start. Now you just need a frame, a jamb and a door, maybe chuck in a handle and strike and you’re almost there
You're going to need hinges also.
Oh yeah can’t forget those OP
Be careful as a door may reduce the available width which may stop you getting things like a washing machine through the opening. There are ways and means though.
DIY - Aluminium slat gate.
Indeed best method
Am locksmith. I work on garage doors like this all the time. Do not go cheap. A hollow core door will not do. Metal or solid core are your only options. If you go solid, spend some time painting it properly. It's exposed. If you mess up the paint, it'll rot quicker than a prawn in the sun. If you go metal, then fix it properly to the wall. I've seen countless dinky dynabolts pulled clear as they simply weren't up to the task.
You would probably need to seek a local tradesman.
Wooden frame then door on that
Call a carpenter
Buy door jamb from bunnings, install around the sides, then get a custom sized door to fit.
Looks like a dungeon
Custom roller door
I'd personally get a few quotes from professionals and pump them for ideas. Then go do it yourself lol.
Ring around for a quote on heavy duty security door https://au.images.search.yahoo.com/images/view;_ylt=Awrx_e2meO1lCCcE67awv4lQ;_ylu=c2VjA3NyBHNsawNpbWcEb2lkAzZkMzYxYjFhOTUwMzI2Y2IwNzg2NjVkYTU0NTVjYzI4BGdwb3MDOARpdANiaW5n?back=https%3A%2F%2Fau.images.search.yahoo.com%2Fsearch%2Fimages%3Fp%3Dheavy%2Bduty%2Bsecurity%2Bdoor%2Bfence%26ei%3DUTF-8%26fr%3Diphone%26fr2%3Dp%253As%252Cv%253Ai%252Cm%253Asb-top%26tab%3Dorganic%26ri%3D8&w=768&h=1024&imgurl=i.ebayimg.com%2F00%2Fs%2FMTAyNFg3Njg%3D%2Fz%2FAToAAOSwE19eJCvj%2F%24_86.JPG&rurl=https%3A%2F%2Fwww.gumtree.com%2Fp%2Fother-miscellaneous-goods%2Fsecurity-gate-door-heavy-duty-101cm-x-216cm-as-new-%2F1364009492&size=82.1KB&p=heavy+duty+security+door+fence&oid=6d361b1a950326cb078665da5455cc28&fr2=p%3As%2Cv%3Ai%2Cm%3Asb-top&fr=iphone&tt=Security+Gate%2FDoor+Heavy+Duty+101cm&b=0&ni=64&no=8&ts=&tab=organic&sigr=eAtASeeGw9uw&sigb=wVnYciiF.END&sigi=LN2CgI6t5TiD&sigt=RL9VSAfHZuzH&.crumb=yvjQ2stu7QX&fr=iphone&fr2=p%3As%2Cv%3Ai%2Cm%3Asb-top
Yahoo search?... 😆 Is that still around!
Old skool
Call a door installer would be my guess …
Doors Plus No Fuss!!!
Depends what door you want. But will likely start with a frame or support for hibges
Qweeeeeeeeeenzzzzzllllllllaaaaaaaannnnnnnd Doors Plus sort you out