Yes, it's one of those problems that follow Murphy's Law I'm afraid Simpbow, the best buildings to take photos of are always discovered on days when the sky is bleach white!
Notmuch you could have done other than bring in a sky from another picture (perfectly acceptable and has been part of photography since the days of Ansel Adams and other such greats!) but if you live close by then of course there's always another day.
The blue monochrome tone you have used gives it a cold dark feel, a little too dark IMHO as it is detracting from the detail available in the stonework. Also, by making the building seem darker, it accentuates the brightness of the sky in contrast.
I think you could crop a fair amount of the sky at the top as it doesn't contain anything of interest, just more of the branches. You could give this a letterbox dimension but I would also lighten the building to avoid the resulting image being too dark.
I applaud the fact you ignored the rule of thirds and went for a centralised mirror type image here as it works fine with the walls' curves leading the eye in. If possible, could you take the picture from a slightly higher viewpoint? This would strengthen the curves and make them into stronger lead-in lines through to the entrance, taking the viewer's eye through the picture.
Just a couple of thoughts, I hope they are of some help to you
Cheers,
Rob