Can't do a Volume Rebuild

I guess my question is... How much free space is needed to do a Volume Rebuild?

I have a MBP running OSX 10.11.6 It has a 1TB SSD with 573.2 GB free. When I try to run volume rebuild it stops during step 2 and says I don't have enough space. My E drive is located on a 2nd 2TB drive connected by USB

Help...

Dunc