There are many limitations on what you can do, depending on whether your proposals are on land which is Article 1(5) land (for the purposes of the General Permitted Development Order 1995).
It also depends on whether any element of your proposals extends beyond a principal or side elevation of the existing dwelling house.
And again how close any of these will be to the highway.
And the existing ridge and eaves heights of the property.
In addition – reference the glazed elevation – Schedule 2 Part 1 Class A(A.3(a)) requires that:
“A.3
Development is permitted by Class A subject to the following conditions—
(a) the appearance of the materials used in the walls, roof or other element of any exterior work must so far as practicable match the appearance of the materials used in the majority of the equivalent element of the existing dwellinghouse“
So unless you’ve already got a largely glazed rear elevation, I doubt you’ll get away with PD rights.
Am happy to help professionally if you’d like.[/url]