Evey Hammond: And you're going to make that happen by blowing up a building?
V: The building is a symbol. As is the act of destroying it. Symbols are given power by people. Alone a symbol is meaningless. But with enough people, blowing up a building can change the world.
Valerie: I remember how the meaning of words began to change. How unfamiliar words like "collateral" and "rendition" became frightening, while things like Norsefire and the Articles of Allegiance became powerful. I remember how "different" became dangerous. I still don't understand it, why they hate us so much.
Delia Surridge: You've come to kill me, haven't you?
V: Yes.
Delia Surridge: Thank God.
Delia Surridge: Is it meaningless to apologize?
V: Never.
Delia Surridge: I'm so sorry.
Lilliman: Please, have mercy!
V: Not tonight.
Answer: Nothing is ever revealed about V's history before Larkhill so we don't know why he was there. As for the roses, in the original comic book, in order to keep him compliant during his time in captivity, V was allowed to tend a small garden while his health was monitored. It was during that time that he first grew the Scarlet Carson roses and also surreptitiously obtained the chemicals that he would use to destroy Larkhill and make his escape. Whether this can be considered consistent with the film storyline is an open question - certainly nothing in the film actively appears to contradict it.
Tailkinker ★