hi!! I'm glad to hear you are working on things! And That is a very good question I ask myself the same very often. for me, it depends on who is gonna use the board. If there is no need to be more specific about the buildings (because sometimes there is nothing said on the script or background designers are still working on it) you can just show the angle and do boxes, maybe throw a couple of small windows to make it very clear it’s a building but that’s all. In my job i could get away with something like this because the layout and background artists are the ones making it very pretty for the final thing. It is clear that i want a city full of buildings for this shot. and I usually just don't have the time do it more detailed tbh.
But if you want to show light sources, and since it’s the opening shot and maybe you want to be very clear about the kind of city it is you can do it more detailed with shading like
or in the style you are using for the board, very cartoonish or only with black lines etc.! (I’ve seen boards that use concept art for backgrounds and it also helps a lot) The idea of a establishing shot is to give an specific mood and place, and if you are the one designing you can throw that there.
This twitter thread is very good in showing the difference between storyboard and layout, with the second tweet having how the board looks!
Hope it helps, and good luck with your project!