Hi, I know there are so many things to take into account and it's hard to get perspective from a photo. The white you can see is an extension with building paper, and the red is the existing building which is two story. The exterior is wide weatherboard planking, the windows are silver aluminium with very little trim. The doors in the front of the picture are French doors from bedrooms that will open to an enclosed courtyard ( yet to be built of course) The roof will be a light grey/brown but you won't see it much because of the flat roof style. There will be decking and ballustrades covering half of the new extension.

Any luck choosing a color yet? Any pics you can share to get an idea of what you are working with?

A green roof pairs well with gray and white homes. For a subtler look, pair a green roof with a siding in a lighter shade of green. I think you are on the right track .You have chosen harmonious shades . New paint doesn't have to match existing colors, but it should harmonize. Some general tips are- Green roof - Gray, green, or white house colors. You could use a dash of yellow also.

If you use masonry paint, we could head in a warm greige direction for all of it - not so yellow . .. something that can give you a bit more contrast against the white windows and trim - even 40 does a lot for us . . . what about a blue green gray? You will get a coastal / mod vibe and it will relate to the farmhouse look .. .above bm silver mink http://www.benjaminmoore.com/en-us/paint-color/silvermink and below . . . gilbraltar cliffs . . http://www.benjaminmoore.com/en-us/paint-color/gibraltarcliffs Shingle look siding on the side dormers would be neat to get that cottage mod. . . you can stick with yellow but I don't think it complements the roof tone. With the blue-green grays, the white windows and trim will really pop beautifully. . . You can also go more neutral with a warm gray - greige . . . here's the siding tone http://www.benjaminmoore.com/en-us/paint-color/capemaycobblestone paired with this for brick - http://www.benjaminmoore.com/en-us/paint-color/graystone potential future red windows . . .aluminum pits over time, so if you have just one side you want to try, you don't have to powder coat, you can take a small brush and just do them by hand with latex paint if they are 10 yrs old or more. . . one advantage to gray . . future see [houzz=]