There doesn't seem to be a selection in the weapon drop down menu for ammunition. I am trying to make a Homebrewed arrow and either I have to select Longbow or make in an wonderous item. I almost have a create 2 different versions, 1 for longbow and 1 for Shortbow. 

Yeah, ammunition has been weird and sort of unfinished since the begining.

I think it will get fixed when they change homebrew, but that is still a ways off.

Inventory on Character Sheet lets you make custom items. Create a custom arrow there for tracking amount.

On Attacks section on Character sheet it lets you make custom attacks. Make a custom attack to simulate the relavant bow with relevant ammo.

The Homebrew tools will be revamped, until then use above. Still better than pen and paper.

Thanks