small office space

I have planned to get rid of the people getting in and out my house by building a small office space next to my house. I would like a small space with all necessary amenities like toilet, meeting room and so on. I do not know whom should I contact for the construction work to be done for the office space. I had a talk with the Jiffy Storage at Canada who seems to say that they can provide me with the perfect service in town. Hope it is fine to go with them. Do you guys have any other suggestion?