A. Here are some things to consider about this project. How far out do you want the bay window to extend? Will it fit under an existing roof overhang or will it need its own roof? If you want the bay to protrude 12" or less, I would recommend buying a complete unit. These usually come with a top and bottom panel, and if it fits up under an existing roof overhang, you can avoid having to add a roof over the window.

If you want this bay to have a larger presence, protruding 18" or 24" out from the house, you should consider framing the whole thing and installing individual windows. A bay like this will need some support. You can put knee braces under it, or if you want it lower, pour a foundation and frame a wall to hold the windows. You will also need to frame up a roof over the whole bay, cut back the siding on the house and install flashing.

You should be able to find some plans for a bay window project in the book section of your favorite home improvement store. You might even be able to find some sort of drawings provided by window manufacturers. A word of caution: Although the roof over a bay window is fairly small, it will require some careful carpentry to get the angles and rafters to work properly and look good.