How can I help with this please?
How much did you pay and how old is it?
Ok. So how old is it?
The Consumer Rights Act is in force now and does apply to secondhand vehicles.
You are beyond the point where you had a right to reject the vehicle.
however, a leaking roof would be covered by the demand that the vehicle be of an acceptable standard. They can't just exclude it because it is not mechanical.
Also, apart from anything else, they obviously haven't done the repair properly.
You can ask they repair it free of charge.
There is no prospect of recovering everything you have paid though unless they agree to it.
Can I clarify anything for you?