By the sounds of it, it's a botched loft conversion so is probably a nightmare waiting to happen.
If you're not handy then pay more for a house that's already the size and shape you want, it will probably cost you less in the end.
Avoid loft conversions, unless you're knowledgeable enough to know what's good and what's bad. Many are dangerous, due to lack of fireproofing, reinforcement or removal of roof trusses that shouldn't have been removed without alternative reinforcement.