The fourth-wicket pair held the innings together before Assam's innings folded up in 87.5 overs.
In the other semifinal tie, A T Rayudu's sedate 97 and helped Hyderabad make 246 all out in 84.3 overs against Karnataka.
Batting first after winning the toss, Assam were in dire straits, losing three wickets for 14 runs in 7.2 overs. But Roy and Sharma shared a 155-run fourth-wicket stand to help the team claw back into the game.
Roy fell short of hundred after he was run out while attempting to take a cheeky single.