Log Shipping Disk Sizes
You're confusing some technologies here, unless I'm missing something or misinterpreted.  Log shipping is FAR different than Availability Groups.  

Your drives on the secondary server do not have to be the exact same size, they simply need to have enough room for the DBs.  That being said, it's usually a good idea to size things the same across environments that are being replicated.  What if your primary DB grows and you have enough room on the primary but not enough on the secondary?  That will take your replication down and cause things to break.