Roberts was part of the Wales delegation who watched Belgium beat France 4-3 at Stade de France last weekend, in a match controlled by the visiting team.
Only two late France goals made the result respectable for the hosts as Belgium, who lead Group B on goal difference at the halfway stage of the campaign, sent out a warning to second-placed Wales ahead of their crunch European Qualifier.
“When they went forward they were quite awesome and we saw a side that are in a rich vein of form,” Roberts said.
“For 60-70 minutes, until substitutions were made, they were comfortable and it could have been six or seven.
“We’re under no illusions how difficult it’s going to be and what they’ve got, and no one’s got as much height or power as Belgium.
“I don’t think there’s any club or national team that has a centre-back marking on the edge of the box on defensive corners, like Belgium do, so that shows what they’ve got in terms of aerial threat.”
Manchester United’s Marouane Fellaini scored twice to make it eight goals in his last 13 games for club and country, while Radja Nainggolan and Eden Hazard, who will again lead Belgium in Cardiff with Vincent Kompany suspended, were also on target.
But Belgium failed to break down the Welsh defence during last November’s goalless draw in Brussels and Roberts says a lot of work and planning has gone into their defensive organisation.
“We take great credit for the way we’ve defended,” Roberts added. “We’ve not conceded a goal from open play yet and that’s given us a foundation to enter the second half of the campaign. Every time we’ve played them we’ve played the same way and it’s worked.
“They did concede three in Paris so there’s a question mark against them, and we’re aware of what we can do when we’ve got the ball.
“We didn’t quite capitalise in the away game but if we can have that extra bit of quality going forward we can cause them problems.”
Watch Wales v Belgium, live on Sky Sports 5 on Friday from 7pm