119 x 19mm TG&V boards to car port roof - advice please

[Sam Maguire]

Total car port size = 9.6m x 3.6m
Roof pitch circa 9 degrees and will be fitted to and between main house and boundary wall.
Main frame to be 175 x 44 @ 600 ctrs on hangers on ledgers both sides.
For aesthetics we are going with treated 119mm x 19mm t&g boards onto the joists and exposed below. Cost a bit more and labour intensive but that's the finished look we want.
Just a couple of queries:
I plan to top fix the t&g boards to the joists with 2 no. 50mm lost head nails per joist. I don't need to hide the fixings so though this would be easiest as opposed to secret nailing. With 4.5m lengths of treated t&g I think I might struggle to get all the interlocking joints good and tight so was avoiding secret nailing via the tongue. I am reading that ratchet type clamps might help - are they worth considering ?
Do I need allow for expansion of the t&g sheeting anywhere particular close to walls ?
EPDM roof to be bonded to to t&g sheeting. Firestone 1.14mm.
Open to all suggestions please about any aspect of the above.

 

[catlad]

Never seen those boards! whats wrong with using the normal 2400x600 0sb3 TG boards?

 

[Sam Maguire]

We like the look of the boards from the underside which will be exposed. Purely aesthetics.
Not unlike alot of the carport / garden rooms that can be purchased online.
I see from online videos that board installation starts on the lower side and work upwards ?

 

[datarebal]

sounds more like a french train

 

[Sam Maguire]

See photo

 

[catlad]

It that's the look your after then use floor boards.

 

[Sam Maguire]

I guess they are floor board sizes except they are treated which I thought would be wise with the underside exposed and open ends to car port.
Any advice on the queries raised ?