Guinsoo was better than scepter on Ogre before, and it's still the best int item, imo.
Still, Guinsoo's pieces are pretty pricey and Ogre (even if he has a great attack animation and a bunch of hps) is not the best farmer in the game.
The solution is to farm an Orchid before then go for Guinsoo if the game last longer. Orchid pieces are easy to obtain, and they gives Ogre mana+mana regen and a bit of dps too.
Orchid is a solid item on Ogre, giving him 60dmg, +30%ias, 260 MP and 225% mana regen plus Soul Burn. Combined with Bloodlust (50% IAS and 15% MS) it turns Ogre into a nice secondary dps source, giving him great support potential too (spammable stun, AoE snare, silence). Imo, Ogre is not meant to be played like a subpar Zeus, since he is so beefy, has a chaser skillsuit and has a spammable steroid spell too.
Guinsoo is the perfect luxury item on Ogre.