Dont be rushed into hasty decisions because of your eagerness to gain 21p by the August 1st 2012 deadline,
It is simply not worth it. "Act in haste, repent in leisure......"
Decide what your priorities are.
Do you want to create a complex roof with 2 dorma windows that will enhance 2 rooms in the rear of your property, yet inhibit the potential generation of electricity that could be generated from your property via a well designed solar system installed on your sloping rear roof.
Changing the design of your rear roof will affect the ability of a solar system on it to generate electricity, because of roof space, shading etc.
Learn how the sun moves in the sky around your property, at different times of the day /year.
Learn about your houses orientation and the various roofs on it.
Evaluate the approximate size of roofs on your property.
How many panels could be sited, on each roof, in what formation?
Does your single garage get the sun?
How big is it?
Is it a suitable solar location?
Ask basic questions and do your research.
Dont worry about August 1st 2012.
Worry about getting it right.
Plan what you are doing properly.
If I was you i'd focus on dealing with the builders first and then worrying about the solar system 2nd.