"As much as you can build" will pretty much guarantee that you have enough.
If it includes both "large openings in the walls" e.g. oversize openable windows and/or sides that are mostly or all mesh *and* "slots maybe 6-12" high and most of the length of the walls, located at the very top of the walls just under the eaves", then you will be in an excellent position to easily manage both summer temperatures and winter ventilation-without-draftiness.
In your location you *can* probably leave a window partway open during the winter if absolutely necessary, although the coop will get awful hot in the summer if that's all you have so I wouldn't recommend it.
Of course, if you don't have many chickens in there you will not need as much ventilation as if you have a lot.
I will stick with the general ballpark recommendation on my ventilation page, which is that in most climates (not the very hottest) you are unlikely to go wrong by having at least 1 sq ft of ventilation opening per chicken, or in an underpopulated coop 1 sq ft of vent opening per 10 sq ft of floor space. Sometimes you can get along just fine with less than that, but often *not*, and there is absolutely no harm in having *lots* of ventilation available to play with.
(e.t.a. -- I would steer you away from those round soffit-vent type things, or anything constructed using a hole saw on your drill. The actual area of a 3-4" hole is very small (not to mention the constricting effect of the edges of the hole on airflow) -- it takes about 12 holes 4" in diameter (which is bigger than most people would make) to equal just ONE square foot of opening i.e. an opening 12"x12". And a typical coop needs a lot more ventilation than that. Really, largeish rectangularish openings, closeable with a flap or slider, are by far your best bet)
Good luck, have fun,
Pat