I’m having trouble with the migration, but first let me describe what I have done.
Since my Aperture database is 380 GB and I only had 120 GB free in my MacBook Pro I copied the entire Aperture Library to an external HD and then deleted the database in the MBP. After doing this I checked the HD using Disk Utility and did some repairs (had run Disk Utility before starting the process and found no problems) and I currently have 535 GB free in the MBP. I have repaired the database and permissions of Aperture after it was moved to the external HD.
When I open Lightroom CC>Plug-in Extras it shows I have 143,972 MB free, so my first question is where has all the extra free space gone? The disk space required to import all 32,352 files in the Aperture library is 322,850 MB so it supposedly has no space and the IMPORT sign is greyed out.
Of the Options I have checked these: Import only applied keywords from Aperture; Create Lightroom keywords for color labels and Create Lightroom keywords for stacks.
Any idea why Lightroom does not see the 535 GB i have free?
What does Disk Utility report now? I see the figures before your copy, but not after.
Disk size may be limited by corruption (which should be resolved if you ran disk repair), or items in the trash. View your trash and empty.
Also, you may not need to worry about space if you relocate your masters to referenced, instead of managed files. This is a recommended method anyway, because you can maintain more of your aperture project or date structure among your files.
As you migrate, it will copy any "managed" images, and leave "referenced" images in place. Suggest you read John Beardsworth's conversion guide.
Be aware there still are other issues with the migration, so read up on that before you begin.