If you do not want your staff and customers in the cold to go, you may consider to provide shelter "special smoking" even though you are under no legal obligation to do it. But, hey, it's not as easy as may seem and there are rules and regulations you must follow if you do not want your fingers to get burned:
Your shelter should be "closed" or "substantially enclosed" In short, a site considered to be included if they have a ceiling or roof and completely enclosed (except for doors, windows or roads) - or permanently or temporarily. Tents, tents and similar structures will also be classified as an enclosed area if they fall within that definition.
The building will be considered as a large enclosed 'if they have a ceiling or roof and there are permanent openings in the walls is less than half the wall area. This is known as the rule of 50%. (A roof includes any fixed structure or moving, like a canvas tent).
Check for a building permit
You have to see if planning permission is required for your residence or whether the outside area you plan to use is covered by the existing planning permission.
Approval may be required for any form of extension to commercial building (such as a garage or covered area) or free-standing shelter. Even if the retractable roof, you may still require permission. You should also consider proximity to your residence doors and windows of your building and your neighbors.