From time to time you might need to create partitions manually in order to install Ubuntu on a specific hard drive in a multi-drive PC.
Get started by deleting all partitions on a specific drive
Next, create a new partition with size 537 Mb:
Format with EFI System
Next, create a new partition with the desired size:
Format with Ext 4 and select mount point as /
Finally,
Install Ubuntu by selecting the root hard disk /dev/sda or /dev/sdb