We'd like to build a small extension under permitted development on a brick and block cavity wall Bungalow on a thick concrete raft. We hope to clad the whole building with weatherboard so was hoping I could DIY the extension in timber. I'm no builder but a good diy'er with good wood skills as I used to repair wooden boats. I'm just not versed in the details of building construction. The extension would be about 2.7 by 4,.5 metres wide with a pitch roof. Any advice - dont do it, get on with it etc. I guess I need to speak to building control to see what floor they will accept, i.e. More concrete slab (its very thick) or foundations and joists. Its not a very warm bungalow despite the cavity being filled, we may put some thin insulation in when cladding (which apparently I do need permission for). How do i match and hopefully improve the thermal in the timber frame and avoid cold bridging through the timber frame please?