Design the space. Deciding on the size, shape and layout of the new room will dictate whether or not additional support will be required. This process may require the professional input of an architect and a contractor. Though more expensive, getting a professional opinion will most likely save money in the long run.
Obtain permits. Once the design and layout are finalized, permits must be obtained. Each state will have its own requirements. This information will be available from your local permit office, and most contractors will be familiar with local codes and rules.
Install substrate. A substrate is a solid, stable surface that must be laid before any construction begins. This process may require the removal of roofing material in order to add a sufficient base for the new room.
Stand the first wall. This piece will need to be anchored into the substrate, a process that will vary depending on local building codes. This anchor must be placed firmly, as instability may create problems when building the other walls. Kicker boards should be used to hold walls in place until framing is complete and walls are fastened together.
Frame the roof. Once the walls have been fastened, the roof should be framed and sheet rock applied. All four walls should have sheet rock applied at this time.
Apply flashing. Flashing is a water-resistant material that should be applied at all joints and projections. These areas may include edges of windows and doors as well as along the foundation. These areas are common points for water entry, and flashing creates a form of drainage to pull water away from the room. Applying a sealant over flashing and over nail heads adds an additional layer of protection.
Apply exterior finish. The process for exterior finishing will vary depending on which style is chosen. Once the exterior is finished, flooring, insulation and sheet rock should be applied to the inside. Select materials that are lightweight wherever possible to avoid weight problems later.