Slightly OT - cost of a 3m x3m extension

Any rule of thumb for roughly estimating building costs?
Having a dodgy back, I draw the DIY line at lugging bags of cement and bricks about so looking to get a builder in for this one.
I'm after extending my dining room out into a 3m x 3m concrete tiled roof/brick sun room witha large picture window on one side, patio doors on another and third wall left as brick. Never had anything like this done before so just wondered what sort of price range I can expect (live in Yorks).
TIA Midge.
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