Michael O'Neill's men had already reached the knockout stage as one of the best third-placed teams, but needed the Republic of Ireland's 1-0 win over Italy to confirm it would be they and not Turkey playing Wales next.
"Northern Ireland are more physical than Turkey," said Coleman. "They get the ball forward quicker - that's where their strength is."
Coleman added: "They are superbly organised and defensively so difficult to break down. They are excellent from set-plays."
Wales sealed top spot in Group B with a stunning 3-0 win over Russia, following an opening victory over Slovakia and narrow defeat to England, while Northern Ireland lost 1-0 to both Germany and Poland in  Group C but progressed thanks to a 2-0 win over Ukraine.
Coleman says his players ended their alcohol ban with a barbecue party for family and friends after their superb performance in the group stage.
"It was great as we had not had a beer since we had been in camp," said Coleman. "Some of the senior players came to me in the dressing room as we had one can of beer each in the dressing room.
"They came to be and said 'can we have one beer back at the hotel? Then we will call it a night as we are playing on Saturday'. I didn't have to say 'don't be stupid' or anything. They took care of that.
"Then it was a great atmosphere at the hotel, all the kids were there. We all needed it.
"The chefs did the food. I don't trust any of us. I have done a few barbecues myself in my garden, but I am not sure I could give the type of burgers I dish up to our lads."
Midfielder Joe Ledley fears he may have run out of celebratory dances following the routines that went viral on social media after qualification was secured in Bosnia-Herzegovina last October, and again in Toulouse on Monday.
Ledley's routine following the win over Russia has been viewed more than 175,00 times on BBC Sport Wales' Facebook page.
"I had them in the locker," said Ledley. "Obviously my mates back home know the dance moves and what I'm capable of doing.
"I just needed the occasion and Russia was that. I just wanted to enjoy it. But I'm not sure what I've got left!"
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Manager Chris Coleman says Wales will be prepared for Northern Ireland's physical approach when they meet in the last 16 of Euro 2016 on Saturday.