roof for the two storey is flat roof, how much to change that?

[midnightOK]

viewed a house yesterday, which had a two storey extension done ages ago. The roof for this extension part is flat. I am wondering how much or how big a work that would be if we have the roof connected to the main roof and make it pitched roof? not sure if that will cost huge amount of money? any ideas?

It would depend on the size, any planning constraints, the tiles, the shape of the roof and how it joins together.

Slate tiles are more expensive than concrete.

I'd say it's not going to be cheap. You'll need scaffold putting up which adds up. Does it make much of a difference? Once inside you can't see it.

You may as well go for a loft extension if fitting a new roof. You would need planning permission.

Thanks @fruitbrewhaha and @Rollercoaster1920 for these very useful information. Really. Appreciate ur help