"Can you reuse the foundations and GF walls of your bungalow"

VAT may not be reclaimable if you reuse the walls

Timber frame all the way for me, though I'd use a small local co, not some big name like Scotframe

Novel build approaches like ICF are wonderful and all, but try explaining how your house is built to a bank or insurance co when you want a normal mortgage to take over your cripplingly expensive self build mortgage, or explain how it would be rebuilt

Also, I know it's tempting to whack clever plans in that make max use of space to squeeze a 5 bedroom house in or whatever, but consider how your house will be rated for council tax purposes when complete. You'd be better off making it as normal and small (2 bed) appearing as possible for completion and assessment then extending into the loft void (because you deliberately didn't choose trusses, and you had the framing for veluxes put in but you roofed over it etc) or cellar, garage etc afterwards - council tax is only reassessed when a property is sold. Saving X hundreds every month for the rest of your life makes sense to me

You can only make a VAT claim once, so if you run short of cash and you're DIYing, try and get the materials in even if you haven't fitted them by the time the claim comes