“We just want a roof over our heads”
A roof only marquee or awning will provide this. Perhaps in England these are most appropriate in the hottest months of July & August.

It is hard to effectively heat an open sided area so a roof only marquee may not be much use outside the summer months, though in a lovely sheltered garden they will maximize the views for your guests.

To be safest though, why not have a marquee with as many transparent walls, windows or French doors as possible.  This way you can open and close sides as required, and enjoy the garden whatever the weather.

Basic 6m x 15m roof only marquee with no floor or lining