After several tries at a ventilator/skylight, have found one I'm almost happy with. As I was asked earlier to explain 'how'...here goes, sorry if this sounds like an egg-sucking lesson and apologise for the length of this post.
1 Using a graph paper printing site, or similar, make some lined paper with 2mm (6" scale) spaced lines of 3point thickness and print in dark grey. Put that print-off in your printer, and in Photoshop or similar overprint in vellum/ingres texture, light yellowish at 50% transparency. over which you have randomly sprayed medium grey to give a mottled grubby off-white effect. This is your aged white, 5.5" tongue and grooved wood. Useful for all sorts of things. Using the end of the roof as a pattern, mark out the ends of the skylight on 2mm mount board, add the sides and cover with the paper. Cover a strip of thin card for the top [TOP TIP.....save cornflake packets or similar, NOT for the card as such, but for the beautifully formed straight folds which make a long thin folded component a doddle, I use it for all my smaller roofs]. Make ends and side covered with yourpaper.
Now....this took the longest to work out.
Give up on acetate film for the glazing.
Cut the material for both of the glazed panels in one piece, from 1mm plastic glazing sheet similar to that sold for green houses etc.(Yes, I know it's over scale thickness...) It's pricey, so I scrounged mine from a sign-maker. Accurately scratch the lines that your bars will take up on the plastic with a sharp thingy and then wash clean of finger grease, dust etc and dry.. Cut enough 2mm strips of paper from your grubby white paper to form all the glazing bars, and then get a bit silly.....
Pour some liquid super glue into a tin lid, or other suitable flat shallow container, spread it out, and holding both ends of your strips, dip/run them through the shallow puddle of S'Glue. Lower them over the plastic sheet in the right place and let go! Count on making 2-3 attempts before you get a reasonable one!
You can press them down with the end of a needle/pin. When they are all done and dry, cut through the middle with a fine saw and wrap and glue (PVA) the ends and top strip. God, that sounds never ending....
Glue the assembly onto the roof (S'Glue gel) and cut carefully round the inside. To do the lead flashing, cut the gum strip off of Rizla papers, lay/hold in place, with tweezers, and stick down by wiping over wth a small SOFT paintbrush dipped in water and shaken out. Rub over with a 4B lead pencil when absolutely dry. If you want a lighter grey lead, rub over/polish with a cotton bud lightly moistened with meths.
Well, hope that helps......anyone know how to wire Peco diamond crossings????????