Is there any problem with adding a vertical brace frame to a column where the top of column is connection to the roof framing via vertical slotted connection (doesnt supporting gravity load from the roof and allows deflection in the roof beam).
Does that mean the forces in the working point of the brace at roof level need to be transferred into horizontal components only since there cant be a vertical component?
1) Having a slip joint be your braced connection is nasty. If at all possible, I'd try to find a way to not do this. That said, sometimes one is stuck with these kind of situations.
2) I don't know that it will be feasible to place the brace work point concentrically in this scenario unless you're willing to:
a) Forgo vertical slip between the brace and the beam or;
b) Have multiple rows of slip bolts which would be pretty strange.
I'll offer up the detail below as one possible suggestion. Naturally, I'm doing a lot of guessing when it comes to your particular situation.