True to their history, whippets are house dogs. They are not psychologically or physically suited to being kept in a yard and they are not especially happy as kennel dogs. They certainly enjoy (and need) a daily romp in the yard or an hour or so spent stretched out in the sun, but as a rule, you should not plan to leave your whippet in the yard while you are gone all day.
Because of the low percentage of body fat they carry, these dogs have very little natural insulation against the elements. They overheat rather easily and they suffer terribly from the cold. In the winter a coat or sweater should be provided. If you don't plan on keeping your dog in the house, you should choose a dog more suited to outdoor life.