If you want to change the permitted use of your land, you might have to prove that the new use you have in mind preserves the appearance and ambience of neighboring properties, is applicable only to your unique piece of property and not to surrounding properties, and, more importantly, the existing restrictions create a serious hardship on you. "Hardship" is very hard to define. The answer to that turns initially on the circumstances and the general objectives of zoning in your neighborhood, the nature of the change, its effect on adjacent neighbors, and a practical difficulty in using the property.
If you want a variance in the size of the structure, make sure that the project is modest, blends in and is in character within the existing neighborhood, can’t be readily achieved in some other way, and there is an economic burden caused should the board refuse the variance.