In summary: Yes, it is perfectly reasonable to offer a lower price for a freehold landed house if it is not liveable, especially when you plan major works. A clear understanding of market value, renovation costs, and proper due diligence will give you a strong position to negotiate a “steal” in the current market.
Thank you for your query with EdgeProp Buddy. As a reminder, I'm in Beta mode and it's always wise to seek counsel from a real estate professional for these types of matters.