Thanks for your perfect reply- I just wanted to check that you do indeed have a Tenancy rather than a Licence (which would be the case if there were shared facilities).
Verbal tenancy agreements do still create legal tenancy agreements which is good news for you. They aren't recommended as the tenant and landlord can find problems occur, for instance with rent payments and deposits/repairs!
Once a landlord has accepted rent from a tenant then a previous verbal
agreement now becomes a legal agreement, so this is the legal background for you.
You do have therefore what is known as an Assured Shorthold Tenancy, and with this, comes various rights, including the right to live in the garage which is kept in good repair by the Landlord- so, if there are any major structural problems/leaks to the roof, the Landlord is under a duty to repair provided he has been given notice.
Your Landlord should have obtained Building Regulations approval for the conversion of the garage (as opposed to planning permission), which is basically consent from the Council that the works have been carried out, as they should be.
As a Tenant, you take the property "as you find it" so you have no comeback on your Landlord in this regard, and legally all he is required to do is to provide you with a Gas safety certificate every 12 months.
I hope this assists, but please feel free to ask further, if you require any clarification.