I often see newbies split exterior architectural renderings into equal halves, with the horizontal line or maybe a distant shoreline extending right across the middle of the render. The viewer, then, is left to decide which half of the architectural renderings is most beneficial, But that's for you - the architectural illustrator - to decide when composing your rendering! Keep this in mind as you compose, instead of cutting the composition in half. This will force you to decide: Which is more important, the land or the sky? Or the water?
An architectural rendering's visual weight (the most appealing things in the rendering) should determine where you place the horizon. With the Rule of Thirds, you can place the horizon line on the lower third diving line or the upper third. And you can adapt the Thirds principle as necessary. If things are exceptionally dull overhead or down below, even a third of the frame devoted to that space could be too much. So you can be more extreme and place the line extremely low or high - say, a thin trip of the sky or landscape.