The PHB entry for the "Ram, portable" (page 153) says that you get a +4 to your strength check when you use it to break down a door. However one of my players contacted me and asked if he could use it as a combat weapon.
I figured that since his barbarian character would be essentially swinging a log at people, that it would be thematic and I decided to allow it. However when I tried to find an equivalent source of damage (i.e. what type of dice the Barb should roll) I found nothing.
What I know is that it will deal bludgeoning damage and be both two-handed and heavy. However what I am wondering about is whether I should impose some sort penalty to the attack role for using an unwieldy item? What is an appropriate damage roll (obviously it needs to be greater than the 1d8 quarter staff)? Should it have a knockback effect? Should it do more damage to creature to creatures huge or bigger (like the siege effect that some monsters have deal bonus damage to structures)?