Garden room/timber frame/bifolds

[cdbe]

I would frame it with a 6mm X 150mm steel plate frame (my place has stock sizes so I generally pick something I consider to be "hefty" enough), wherever you can fit it (inside or outside). A steel place will weld it up and deliver it - just screw it to your studwork.

 

[big-all]

the idea off metal is to stop the corners flexing and acting like hinge points
you may be absolutely fine without extra support as most off the load when static is on the wall each side when the open door leans to wards the back or forward iff outward opening
its when moving the doors sideways and as said with wind load or even hanging heavy things on walls near the opening
if the brackets will be in the space the doors will be fitted in rather than a to the side retrofit with doors in place, it's best to sort out now whilst it's easiest

 

[23vc]

Good points, thanks. The brackets /brace can be fitted after the doors as they’re flat surface plates. I’m also now thinking I should add more /bigger screws to the roof OSB which I can still do as it’s only got a dpm covering it for now. In my mind the roof is shearing despite being sheathed so thinking that may help. The ceiling joists also don’t have any noggins which may or may not help

 

[big-all]

they will need to screw into solid timber firmly affixed to the uprights they won’t have to be much more than perhaps 12mm thick perhaps 60mm wide and perhaps 400mm legs ??
but wait for others to comment as its fully a guess