I want my conservatory to be a sitting room, anyone got a magic wand?

[UriGeller]

The conservatory has a concrete floor so my main question is does it still need foundations building? And is £15,000 a reasonable estimate? It already has power and a central heating radiator and is about 4x6 metres.
I'm dying to get on with it as it means the current sitting room could become a lovely spacious new bedroom for when the folks come at Christmas.

Does anyone have knowledge or experience of a project like this?

Can you provide a few more details. What kind of structure have you currently got (what are the walls and roof made from?) and what do you want it to be?
Glass weighs less than bricks/roof tiles so you may well need to strengthen your foundations.
As you currently have a radiator in there, are you sure it's a conservatory?

What are you planning on doing to it to make it into a sitting room? We had a conservatory and investigated options such as putting a 'proper' roof on it in order to make it usable all year round. In the end, the best course of action for us was to demolish it and replace it with an extension - which needed new foundations. It would have cost us around £15k-£18k IIRC to convert/insulate the conservatory to a sort-of living room and it cost us around £25k to get rid and build a proper extension.