Extension

Hi, I am looking for some advise on extension roofs! I live in a bungalow and am looking at having an extension put on the back where the kitchen is. The back of the house has a gable end. This comes down quite low, and the kitchen/ extension would be right at the end of this gable. I would say it comes down level with the wall itself (I hope this makes sense!). Our budget is my main concern and what roof we should be looking at. Would it be cheaper to inset the kitchen a bit and have a flat roof or carry on the existing pitched roof on that side of the gable and and have a pitched roof?? I really hope you can picture what on earth I am going on about! Thanks