Like, sitting on a plate in front of him before him, or like standing in line and the sandwich is first? Previous lessons suggested that riomh was related to time (ie: i eat before the boy)
I put 'the sandwich is before him', meaning in front of him, but it's marked wrong, isn't that a bit pedantic?? We do say 'we place a meal before someone'.
roimh doesn't indicate possession - you might make a case for "he's got a sandwich in front of him", but just as "there's a hole in the ground in front of him" doesn't imply that he owns the hole in the ground, "there is a sandwich in front of him" doesn't imply that the sandwich is in his possession (though in most cases if someone puts food in front of you, there is an implied permission to eat it).
roimhe is a "prepositional pronoun", a combination of the preposition roimh and the pronoun é.
romham - "before me"/"in front of me"
romhat - "before you"/"in front of you"
roimhe - "before him"/"in front of him"
roimpi - "before her"/"in front of her"
romhainn - "before us"/"in front of us"
romhaibh - "before you (plural)"/"in front of you (plural)"
rompu - "before them"/"in front of them"