So the Official Translation released, and the context of how it is worded is definitely interesting.
Ace says "That's at the end of my little brothers dream." "I really think he can make it happen."
What we can gather from that is that it is something that can only happen after Luffy becomes Pirate King, and apparently, Roger wanted to do the same thing. Luffy also said this in front of Shanks, as Shanks told Rayleigh that Luffy spoke the same exact words Roger did.
All these years definitely thought it was Roger saying it was him wanting to be Pirate King, but thats definitely not the case. Given the type of character Luffy is, I can see it being something along the lines of "Once I become Pirate King, I'll throw the biggest party there ever was and invite the whole World."