I know this is tremendously difficult to estimate, but I'll give as much info as possible.
Quality builder (yes, I checked the references). My home is colonial style, c. 1950. It has a 13x16 one story addition off the back. We want to add a 13x16 room above. It will have a gable roof, 30 yr shingles, ridge vent, vinyl siding, 4 Andersen windows. Sheathing to be plywood, not OSB. Heat will be forced hot water fed from the existing boiler. New circuit to provide 2 outlets on each wall, plus 2 lights in in the walk-in closet. Walls will be a veneer plaster system. Floors will be red oak with 4 coats of polyurethane. Trim is pre-primed colonial casing. Actually, it has a few more details than colonial, but the contractor found an almost exact match in the Brosco catalog. Modifications to the existing floorplan: Removing part of a bearing wall and replacing with an engineered beam. Taking space from one room to create a hall. Removing an existing doorway. Adding 2 new doors. Building a walk-in closet. The crew has to carry all of the materials to the site because a truck can't get to my backyard. I'm in the Boston area. Contractor cleans up at the end of each day. Says he will not harm the landscaping. Total duration of the project will be 5-6 weeks.
I don't see how the square foot method of estimating can work, given the differences in quality of construction, materials, etc. Anyone care to hazard an *educated* guess?
Thanks.