I know its a bit absurd to have Windows 8 theme on Ubuntu 14.04. Personally, I prefer Numix Theme on my Ubuntu 14.04. But, in case there are some people who just switched to Ubuntu and still want the look of Windows 7 or Windows 8 on their Linux, this tutorial will show you how to make Ubuntu 14.04 looks like Windows 8. Again, thanks to Noobslab team for providing this theme and icons.
First we need to add the repository.
sudo add-apt-repository ppa:noobslab/themes
sudo add-apt-repository ppa:noobslab/icons
sudo apt-get update
sudo apt-get install win-themes
sudo apt-get install win-icons
Next, you will also need to install Unity Tweak Theme application
sudo apt-get install unity-tweak-tool
Now, open Unity Tweak Theme and select Windows theme and icon from there.
And here is the Ubuntu 14.04 desktop with Windows 8 theme
You may want to look at my other post on Mac OS X Theme on Ubuntu 14.04