Property redesign is no small task, especially is it involves extensions. You are relying on a contractor to understand what you want, work to an architect’s drawings and create a home that you are going to love. It’s also no easy task for you to select someone who really understands your vision.
You may want to get an architect to draw up some plans beforehand, or you may prefer to complete the whole process in one go. This would involve getting an architect to draw up plans along with the builders, so everyone knows what is happening to the property. This is the ideal situation in many ways, but it takes a lot more planning, especially if you are still waiting to get planning permission.
You should choose a contractor based on what they can do for your property, and what they have done previously. Look at their portfolio and talk to them about how they can help you.