Yeah you would get that if you havent allocated room for your root partition /
Are you trying to dual boot with other OS? or are you planning on install Ubuntu in the whole drive?
So when you get to the step of the installation type select the option'something else' there select the partition in which you want to install Ubuntu. Or you can there select the whole available space in the drive and click on the plus sign on the left bottom corner of the dialog pop up and crete a primary partition for / 15 to 20 GB would be fine, format it on ext4 and mount it on /
Next create another primary partition for home select the size you want and format it with ext4 and mount it on /home
Note the home partition should of a good size because there is where all the user data goes. Downloads, Music, Videos, and Documents. So make sure you give it a good size
Next make another primary partition about 2 to 3 GB and select to be the swap type.
Once you have these three partitions accept the changes and continue with the installation.
Post back with any results here so we can help you more if the above doest work.