I've recently finished my loft. Took a wee bit longer that expected (over 4 years but not constantly working on it and job changes/money played a factor!)
Long and short of the job, 50's semi, three sided roof. Added new floor bearers as original floor was laid on the on the tiny 3x2 ceiling joists! Strengthened under eaves onto supporting walls, strengthened roof pitch (where the three sides come together. Job lot of 80mm Kingspan seconds through ebay direct from the factory. Cut to get between the roof joists with 20+mm air gap. Foil insulation (looks like aluminium bubble wrap) over the top of Kingspan. Add two Velux type roof windows, loads of plasterboard, and skimmed as the Bro in law is a plasterer and I now how a lovely warm loft in the winter and a nice cool loft in the summer which was completely bareable last summer with the windows open.
It is a hell of a lot of work, but I'd sooner have my stock above my head than in a shed. Comfy, accessible through a heavy duty wooden loft ladder, plenty of space, no prying eyes through the window (unless they've got on the roof!), TV and tunes straemed up there and room in the middle for the (not quite so) little one to play.
I'm personally glad I went this route!
HTH