This may be of some help/ interest.
I am in the process of constructing a 5.5 MT long by 3mt wide alpine house in timber. It’s the same as a greenhouse but full of opening windows to keep Alpines cold and dry not warm and wet!
My choice is WR cedar Joinery grade. Nominal Timber joist sizes easily available are:-
6”X 1”, 8” x 1” and 8” x2”
Local Merchants were, as many of you said , expensive but I found James Lathams after 6 other quotes and got first class service, top grade timber and saved over £1k! That took some believing. There’s also a chap in Birmingham with good prices but I can’t say further than that .
The 32 windows i have already made from Teak , recycled from a laboratory built in 1945/6 and demolished in the late 60’s.
There will be two sliding doors ( I need them open for 9 months of the year) at either end , made in hardwood but totally sheltered from UV and rain . I am Having no luck so far, in finding an affordable double door slide arrangement. They are either intended for home Interior use with plastic rimmed wheels (soaks up water) or heavy duty for farm barn doors and cost a bomb.
To sort the design out I built a 5:1 scale model . A lot cheaper to change ideas when made from scrap off cuts as well as sort out joints. It did add a further 9 days to the project. The finished sections sizes and structure were reviewed by a fully qualified structural engineer (My son).
I will coat the timber using Sikkens . Wipe the timber with meths, I prime coat , 2 top coats . Should last our life time.
This is my second post, my first( a request for advice), 2 days ago, was totally ignored by everyone even though I know there are people on the forum that could help. Not a good start.