Darren is a fantastic player for us
The goalkeeper is out of contract at the season's end, but moves have again been made to secure his services for longer.
Randolph's worth to Blues was apparent in the 1-0 victory over Blackpool as he made two key second-half saves.
"We have come in so many times after games and probably taken it as a bit of a given, Darren doing something like that," said Rowett.
"But you can look at lots of the games; Cardiff at home quite early in our tenure he made two fantastic saves one versus one and really kept us in the game.
"You could probably go through half our matches this season; he has actually made some brilliant saves to keep us in games or win us games. I have been really pleased with him.
"We've been discussing his contractual situation at the end of the season, we have put a contract offer to him very recently.
"I had a private agreement with Darren that we would let the transfer window develop for him because I felt as though, like any player, they want to see if there is a Premier League team out there that might be interested.
"Everyone is well within their rights to do that. That's a sign of ambition.
"But after the window closed I think it was important for us to sit back down and say 'this is where we see it, this is what we would like to offer you for next year'.
"I want him to be a big part of what we are doing going forward."
Randolph joined Blues on a Bosman from Motherwell in the summer of 2012 and has proven himself one of the best goalkeepers in the Championship.
Asked whether there has been any indication about what Randolph's intention might be, Rowett said not as yet.
But the manager added: "I am hopeful that we might be able to get something agreed soon. Like I have said, he is a fantastic player for us.
"But I have been in football long enough to know until the ink is dry nothing is set in stone."