If Rocco's last ability triggers because a spell was cast, that ability will resolve before that spell does. If the ability triggers because a land was played, the land will be on the battlefield by the time you put the ability on the stack. If the land entering the battlefield causes any triggered abilities to trigger, those abilities and Rocco's ability will be put on the stack at the same time, with the abilities controlled by the player whose turn it is going on the stack first (and thus resolving last).