How you getting on with the build?
I have lesson learned from mine that's giving me headaches now that I thought I'd share. My header beam for the bifold door has sagged ever so slightly which is making the doors more effort to operate. Correcting it now is difficult.
My header (for 3m bifold) is two 2x8s glued together with 2x4 under and above to effectively make 4x12. I suspect it has sagged as it has dried out over the year it's kept dry.
If i were to do it again, I'd layer in a steel box section.