Simon, Read your last post and, feel that this roof is way beyond what you will manage, however will try to elaborate on the advice already given , and explain your problems, but remember we are talking U.K regulations. Have no idea how you work in Portugal. Sizes are all based on max dead load 0.75kNM2.
Guidance is based on overall length 8.6metre, and overall span 4metre with 200mm overhang. Two concrete posts, one each end, and intention of fitting wooden post in centre. No other supporting walls except wall you intend to lean against.
Firstly, one intermediate post would be insufficient, would suggest two number at approx 2.150 centres. with 1.350x100x100 concrete spur bolted front and back, to support wooden bressummer over the 8.600 run length.
After saying that, would feel a lot happier with 100mm box section with plate top and bottom.
You need two, 50xx225mm bolted together with bulldog connectors to form wooden bressummer stood on edge and oblique scarf jointed over each intermediate post
Pitch will be at your discretion, and depending on what type of tile you are using, could be anywhere between 22.5 and 45 degrees
Say 22.5 degree pitch, length of rafter will be from top cut to plumb cut at seat 4.208m long and even working on 50x150 rafters at 400mm centres, they will need a purlin mid span.
4.208 plus overhang makes length of commons 4.5m long, which length you will find hard to source. Your next problem is you have no end walls to support purlin, This can be overcome the old fashioned way, by making up 4 number half TDA trusses with stub toe for building in. One each end and two intermediates to support purlin. Purlin would need to be somewhere in region of 75x225mm.With the centre span purlin you can reduce your common rafters down to 50x100 and use two lengths 50x100 either overlapped or scarfed on top of purlin. but you will need to add blocking plate to bressummer in between T.D.As to obtain H.A.P. for your birdsmouth to match plane of T.D.As. Ditto to purlin.
Even though your run of rafter is a good length, it is still possible to make up TDAs with spliced joints to reduce length of main rafters.
Strap bressummer down well to stanchions with twisted heavy duty restraint each side. With no ends and high wind , whole roof could move. Triangulate bressummer with TDAs. and ditto to stanchions. Triangulate and brace whole roof with 25x100 to underside of rafters above and below purlin.
You will have 4 couples with your TDAs, but would suggest couple every other rafter, unless of course you want ceiling of some sort, then couple every rafter with 47x100 at 400mm centres with 50x175mm mid span binder hung on TDAs. Do not understand why you want shiplap boarding on top of commons.
It is a very easy traditional cut and pitch, but there are problems unless you do not fully understand roofing. Assume you have no idea what I have been talking about, but show it to any chippie who knows cut roofs and he will understand what I mean.
Suggest think along lines of engineered I beams or glulam beams, but you will need someone to design them for you, and they will not work out any cheaper.
Better still, and by far the cheapest, feel sure that you must have truss manufacturers in Portugal. Contact one of them and they will design and quote you for a half trussed roof with stub toe to bottom chord. Sorry that I have thrown so many problems at you, and have not been much help. For guidance only. old un.
