I had a few problems getting things building on my Ubuntu system so i thought i'd make a note of the steps i used here to help others interested in running LEAN on Ubuntu 16.04

1. Make sure your system is upto date

sudo apt-get update

2. Install the latest version of Mono. The Mono project home page has good instructions for various distributions;

http://www.mono-project.com/download/#download-lin

3. Install Mono

sudo apt-get install mono-complete

4. Install NuGet and Python-pip

sudo apt-get update && sudo apt-get install -y nuget python-pip

5. Make sure that NuGet is recent version to avoid errors when builidng QuantConnect

sudo nuget update -self

That was it. Now i'm able to run LEAN on Ubuntu. Hope this helps someone else.