Back to brick with the details you provided is £350-400K. All depends on the spec you want too. Try Doran bros construction based sw17, they did 1 for me ages ago and were the best, speak to Fintan there. He does all big jobs, old school family run co started doing lofts ....
 

Hi, my partner has a construction and frequently undertakes similar projects in the area. I've asked him to give a rough guide, see below:

Loft 80k+VAT
Side return 90-120k+VAT
Bathrooms 8-15k+VAT (per bathroom)
Garden 15-35k+VAT

This is just the build works, excludes second fix items such as a kitchen, tilling, glazing, etc.

Hope this helps!

Hi
We're looking to buy a fixer upper and I know building costs are fluctuating widely - does anyone have recent - as in last few months figures for costs of a

Loft
Side return
Bathrooms
Garden

For a standard BTC terrace.

I know it all depends but we did our last one about seven years ago and for £350k you could effectively gut and re-do the whole house with new everything. I'm just looking for rough costs to the nearest £50k.

I suspect it's now closer to £500k but I really want to know if it's closer to £600k.

Thanks