I managed to fix the image pretty quickly. I'm not sure where to go about uploading it though.
Basically, I used threshold to give me a mask that masked around the upper part of the building. Which I then selected by color to isolate the sky. Next, I took the eye dropper tool to select the sky near the trees and set the back ground to the sky near the top.
Taking those to points, I overlay a duplicated layer with a gradient. This was set to only darken. The results will then need to be touched up for contrast as they're largely lacking in contrast and look a bit muddy, but it's a fairly easy procedure. You won't have any detail in the sky, but if you really need that, you should have exposed for the highlight and bracketed for the shadows.
As for halos just try duplicating the layer and set the top layer to multiply instead of normal in the layers tab, Once done should be a decent little effect, try pressing up and down seeing which blend mode works well and make multiple duplicates with different blending modes. Then using the pen tool, or selection tool or just paint around the edges, make a mask and duplicate it when needed to make the sky levels different to the foreground. Should do the trick Once you have the blending you want then apply levels to each and tweak where needed.
You’ll never be able to do a decent job of masking tonal differences between the layers using a basic layer mask, even with a Wacom. You’re far better off using the advanced blending modes built into Photoshop (see my note to the OP below).
Just set 3 layers, change one to vivid, one to multiply and the bottom to normal. Instant improvement, I have a Wacom I do agree advanced blending will help but for a newb it's a quick improvement and a place to make a start.