House extension and renovations

Hi , Im looking to get some building work done on an old house its a small two bed approx 85sq metres..we want to get a two storey extension done out the back into the garden..does anyone have any ideas how much builders charge per sq foot / Metre , i have heard so many different figures, were looking to get two more bedrooms upstairs plus a kitchen / Diner downstairs and an extra reception room..also we will be converting to gas at the moment its oil heating..any ideas how much that would cost also..any help would be great ...tanx...

If you use the excellent search function, you'll find loads of threads done on this previously.

Just like I did, when I typed in ...

Thanks I,ll try that now