Unfortunately we can't really answer the question as we need to know much more detail about the roof, the measurements, your plans etc.
However we would like to help so you may be interested to know that we have just launched a new design service for our clients. We would be pleased to provide you a quote for feasibility study to assess viability before committing to major project works.
Jeremy Wedge MIstrutE CEng on behalf of Loft Conversion UK