Site Preparation / Excavation
Are there some specific landscape features (like mature or expensive trees or plants) that need special protection? Do you need some tree removal, yard clearing, demolition of existing hardscape (patios, walls, etc.) digging the foundation hole, hauling off unwanted fill, back filling after the foundation is done, and final grading?
Foundation / Framing / Roofing
Figure in pouring the footings, pads, bulkhead access, and/or slab, concrete walkways, insulating and sealing the foundation, framing the walls, floors, and roof with a specified grade of lumber and other materials (asphalt, shingle, cedar, tile, slate, etc.). Is other drainage or is waterproofing necessary?
Exterior Finish / Masonry / Insulation
Think about materials for the exterior of the house (the type of siding, for example, clapboard, shingle, brick veneer, board or batten), the door and window trim, the corner boards, the trim at the eaves (fascia, soffit, frieze, or rake boards), stone or brick facing on the foundation, insulation for the walls, floors, and ceilings.
Electrical / Plumbing / HVAC
If additional fixtures, appliances, capacity of water, heating, or cooling will be required to service your added space, you may need a hot water heater, furnace or boiler, air-conditioning components, or other electrical or plumbing equipment. Do you need additional sinks and faucets?
Windows and Doors
Think about windows in your addition unit situated for a view of the backyard, garden or other preferred area (total # of windows, size, make and model, moldings type and profile etc.) and doors for access to the backyard, patio or entertaining areas (total # of doors, make and model, moldings type and profile etc.)?
Interior Trim / Stairs / Cabinetry / Appliances
Do you need new cabinets (custom or modular, material, stain or color, door & drawer type, custom cabinet accessories (knobs, etc.))? Do you need new countertops (material type, edge detail). Think about flooring (material type, make, model, square footage, baseboards etc.).