Modern U shaped office, grass quality

The grass material used in the scene looks pretty saturated - consider toning that down. As for your render times, are you using proxies in conjunction with grass-o-matic?

Here is an update of my rendering with better quality grass. I used "Grass-O-matic" rather than the "displacement method". THe rendering time has been multiplied by 4. Any other suggestion to improve the rendering quality/computation time ratio ? [ATTACH=CONFIG]43867[/ATTACH]

Not only grass but trees need rework to achieve photo realistic quality.

You can give this tutorial a try; http://www.cgarchitect.com/creating-realistic-grass/ I watched it but haven't actually given it a try so I can comment on how difficult it is to do.

Thank you for the post Robert but the link you provided is not working :confused:

Do a search for different grass techniques on here - there's a ton of threads with several geared specifically to MR. A few I would suggest is Grass-o-matic plugin (free), and use MR proxies. 3D grass is always the most realistic. There are others though, to include displacement mapping, etc (but in my opinion, not as effective). Composition wise, I'd suggest pulling the entire building into the frame shot....right now with one corner leaking off the top of the shot looks odd. Also, you have two trees with spring/summer leaves and then what looks to be a young autumn blaze maple with a fall set. If it's intended to be a japanese maple, the leaves would be much more purple/darker.