Earlier today while playing with Google Drive I noticed they did not display how much room I have left like they do in Gmail. While poking around I did find it. Here is a super quick tutorial on finding how much space you have left in your Google Drive.
To get started open up Google Drive
When your drive opens click on the lower gear / sprocket (Sprocket sounds so much cooler)
When this opens click on settings
On the next page you will see your available space.
Have a great weekend!