Wooden garage door frame

[Lewrr]

I am after some advice on replacing this mental up and over door with a wooden version.

My main concern is getting the new wooden frame plumb, the head section concrete slops and because this garage concrete panelling rather than brick work then the fixing surface area is quite minimal around the current door.

Any advice and recommendation on fitting the new frame would be much appreciated.

 

[Wayners]

I'd buy the frame kit. Assemble it using some cut up hardboard as that can be made into big set squares. Temporary fit strapping to keep frame square while fitting.
Pack screw and fill around.
Then fit door.

 

[Lewrr]

My issue is that the garage is pre fabricated concrete panels therefore it’s only about 50mm think around the door.

I’ll add some more images when I get chance to show the issues, I just wanted to see if anyone had fitted a wooden frame and doors to a pre fabricated opening like this before.

 

[Wayners]

My Marley garage wasn't like that.
Frame held with L brackets.