Hi Inactive User ,
To use google fonts, you shouldn't have to download and add the font file to your community's assets folder. Just make sure you've added the external link correctly to your header's head content, like so; for the font family Source Sans Pro;
<link href='http://fonts.googleapis.com/css?family=Source+Sans+Pro:400,300,300italic,400italic,700,700italic,900,900italic' rel='stylesheet' type='text/css'>
When I'm specfing the font in my css, its written like so;
.blah { font-family: 'Source Sans Pro', sans-serif;}
When adding the font to your custom skin's skin property page font values, it should be entered like so;
font-family:Source Sans Pro, sans-serif; font-weight:normal;
Hope this helps