For post production I had to do more than I initialy intended to, I like to render as much as I can the final image and just tweak some colors in the end but this was not the case, mostly because I didn´t have much free time.
First thing after opening the file was to control all the multipasses from the render. With this I can control some details seperatly and fast: reflections, light, shadows, etc… After that I corrected the overall colors of the image, removing some of the exagerated blue of the hdri. I also darkened the trees in the background and added some dirt to the wall of the lake. Finaly just made a vignette and placed some people inside the building and outside. One important detail was to increase the reflections of the sky in the water to create a better mood and impact in the final image.