Since multiplayer has been added to Stardew, other updates have added additional options and farms to make playing together easier. Once it's plopped down, you can now invite another farmer by starting up split-screen co-op, a LAN session, or sending your invite code. Robin will build cabins instantly, so you won't need to wait any in-game days for your friend to join you. They're quite cheap, so even if you've just started a new farm you should be able to create a spot for your friend quickly by bringing her 100 gold and 10 stones or 10 wood.
Visit Robin's shop to build up to three cabins for anyone you want to invite.
If you want to turn your solo farm into a co-op farm, don't worry.
