This is the multiplayer Beregond deck that I built for Siege of Annuminas, with a Gondor theme. I actually ended up loaning it to another player at another table, so I didn't get to see it in action, but he said it worked really well.
The goal of the deck is simple: beef up Beregond, and defend for the whole table. If another player has some Ranged characters, you can stick a Gondorian Shield or Blood of Númenor on either Denethor or Eleanor, optionally engage a few Enemies, and use your other Heroes to defend as well.
Most of the Attachments go on Beregond, even Steward of Gondor. You could put it on Denethor if you prefer to dole out resources to other Gondor Heroes across the table, though, and the deck would work just fine.
In the late game, you should be able to put out a decent amount of as well, but it takes a little time since you'll need to get either Faramir or Visionary Leadership down, as well as a handful of Allies. Still, it's nice to be able to help contribute to something more than as the game wears on.