Complete refurb - anyone done this?

[ButterMelonCauliflower]

And how much did it cost?! Bit of an impossible question by I'm trying to get a rough idea and whether it's worth the effort. We've seen a house we like but it needs complete internal renovation. It's big - 3 floors, 5/6 beds. Needs central heating, probably new electrics, we would want to install a bathroom on the top floor (there's no water up there at the moment). Replace family bathroom, new kitchen and a decent extension on the side return downstairs. And redecorating, obviously. We would not be doing the work ourselves and would rent somewhere till it was finished.
Has anyone done anything like this and survived?! Was it horrendous? And how much did it cost? We need to get a rough idea before we can offer on the house - are we talking £100k or closer to £200?
We have 2 young children and I do wonder if we're crazy to consider it, but it does seem a great opportunity...

How many sq ft is the house at the moment, and what do you want to extend it to? Where abouts is it?
The rough rule of thumb is to allow 20% of the value of the house for a refurb, but obviously that can sky rocket if there is structural work to do.

If you want to move any internal walls to fit extra bathrooms, there is always the (nuclear) option of completely gutting it, taking out all walls and floors and rebuilding the house internally around a new steel frame. The advantage of this is that you get a new-build house within the old shell, so all plasterwork, electrics, plumbing is brand new, plus you can easily tinker with the wiring.
The tipping point for this being worth doing depends on the value of the house, but generally, once you want to move more than 2 walls, it becomes worth while looking at. It obviously makes the house totally uninhabitable, but it is quick... We went down this option, as did some friends of hours. The trick is to find an excellent architect and structural engineer, and let them project manage the builders (who would need to have previous experience of this as well) Don't visit the house too much as a work in progress..!

We did a three floor complete refurb - 120 metres square. Moved walls and rooms. We have chosen high spec for most of the house (apart from kitchen units) and it cost us approx £180k. We visited the house almost daily and took photographs of all that was going on. That has proved important for various reasons now. It was a stressful time.

*can easily tinker with the wiring
Can easily tinker with the layout! Monday brain in action there...

Complete refurb here. New roof, big extension, new CH, new drainage, floors, windows, in fact pretty much everything £250K. We PMd ourselves though.

Thanks for your replies - looks like we might have to knock their price down a bit!!
The extension would not be huge - at the moment there is a galley kitchen that sticks out the back, we'd want to extend sideways to make it the full width of the garden.
The house itself looks pretty solid and the roof looks fine. I think it's been well kept, just not modernised. Doesn't seem as drastic as what mrsFrancis or sparechange did.
We've done a fair amount to our current house - new flooring, new kitchen, new windows, all with a newborn at home - so it's not like we're complete newbies. But this does look a much bigger job. Would want to get someone to PM for us I think. Or one firm I to do all the work for us. Do you get people who do that? In Reading if anyone has recommendations!!

OP, there are roughly two ways to do it - full service builders, who will bring in all the relevant trades at the right times, oversee all the work and either liaise with your architect (and structural engineer), or appoint their own. This is the least hassle option, but you pay for it. It does mean that you have one point person to go to with any snagging or problems, and it is their job to sort it out.

The other job is to appoint a project manager (or do it yourself) and then find individual trades, and bring them in at the right times. This can be a coordination nightmare, especially if some works overrun (or materials don't turn up on time, or the weather is bad, or if building control don't come out and inspect at the right time...), but you will save a considerable amount over the first option.

We did much the same refurbishment to a 2 storey period house. No load bearing walls were removed and refurbed bathrooms already had water = £70k. We were going to do a small extension, that was another £50k. So total £120k with us managing it.

So you'd need above plus new plumbing, new wiring. You need to budget £150k, another £20k if using a project manager.

We did a full refurb on a five/six bed three-storey house - a new thatched roof had been added already (thankfully!) as had a new boiler, but otherwise we rewired, changed the rads (and had boiler moved), added a large architect-designed kitchen extension with double-height windows, fitted new engineered oak flooring and limestone downstairs, new d/g timber sashes to front elevation, new kitchen and three bath/shower rooms as well as replastering & decorating throughout.....oh, and re landscaped much of the (large) garden We increased the house size from 2000 to 2500 sq ft.

We spent around 100k and used high-end finishes.....but I'm a compulsive eBay shopper, we have friends in the bathroom industry who got us good deals on Hansgrohe, V&B etc and we project-managed as well as doing all labour plus tiling, flooring, plastering, gardening and decorating ourselves......and it took three years

This was in Wiltshire, btw.....