Some files to help you along:

Step 1

Open your model or the one provided in Blender. Make sure the rigify add-on is enabled in Blender by going to User Preferences, hitting the Add-on's tab and typing rigify to bring it up

Step 2

On your mesh hit Shift-A and select Armature > Human (Meta-rig) from the menu. You might need to move and adjust your meta-rig so it lines up nicely.

Step 3

With the metarig selected switch to armature and then under Rigify Buttons at the bottom select 'Generate'. It might take a little bit to generate your rig.

Step 4

Deselect your rig by hitting 'A' then select your mesh and then your rig and hit Ctrl-P and select 'With Automatic Weights'.

Step 5

Delete all of the WGT items that Blender generates.

Step 6

Open up a Unity project and add your .blend file to a scene. Then, open the Ragdoll wizard by right clicking on your object selecting 3D Object and hitting Ragdoll...

Step 7

Assign your bones as shown here and click create when you are done.

Enjoy your new ragdoll - you might need to make some adjustments in Unity to get it looking exactly how you want, but it's a good start.