Without seeing a photo its a little hard to advise so, and apologies if this seems a cop out, but I would really recommend asking the opinion of a surveyor.
From your description it would seem that you have a truss rafter roof so although of course a conversion can be achieved there will be structural issues.
I'm not certain of the level of service that local authorities provide in Ireland but if similar to England than another viable, and cheaper, option would be to contact the local planning officer.
