Stardew Valley has multiplayer, if you're in the mood for something relaxed.
And not a base-builder, but the most fun I've had on multiplayer lately was with Overcooked. Very, very shouty, but satisfying when things click. (Also the best title of its ilk, I'd say.)
I was kind of interested in Stardew Valley, even if it looks like ass, but I was thinking of getting it on console for local multiplayer.
Overcooked is truly amazing for couch co-op, I friggin' love that game. Played it a while back with two friends and it was a wonderful, hysterical time.
Definitely not relaxing in the slightest, though. Not that I'm necessarily after relaxing, but y'know. Oh and I should clarify that I love the gameplay - the progression, not so much. We eventually reached a point where we didn't have enough stars to continue and after a few attempts at re-doing old levels we kinda gave up. In a similar vein, I really dig what I've seen so far of Moving Out - similar levels of chaos and teamwork, as well as tough challenges to do, but it doesn't seem quite as harsh with requiring you to do well to progress.
Anyway, I'm getting off-topic. The Forest looks interesting if I can get it on sale, apparently my PC can actually run it. Green Hell looks really damn cool from the brief gameplay trailer I watched, buuuuut I think I'm just shy of the "recommended" requirements, so who knows if it would work at all. I'm not experienced with this kinda thing and I'd rather not buy a game I can't run without upgrading - I've spent enough (not much, but enough) money on this computer business already, haha.
Ark came up in conversation the other day when my friend was tryna remember the name of some survival game with dinosaurs, but apparently he was thinking of something else. I should ask the fellas if they'd be keen to play that one.
Other ones that look intriguing are Valheim (my friend was kinda hyped when I told him about the boats) or that game where you play as kids shrunk down to bug size in a backyard, but I don't know if I could run 'em. This Scrap Mechanic game I just came across looks like it might fit the bill, too. Apparently I meet the recommended requirements, which is a plus. Anyway, I'm gonna get back to looking through the co-op section of the Steam Autumn sale.