Originally the Scots had wanted to keep the roof open while Wales were keen for it to be shut, with the atmosphere in the stadium extra special when it is thus.
Under Six Nations regulations, the roof is only closed if both teams agree to it, which meant it was set to be open for the final fixture of the opening round.
However, Scotland?s U-turn a day before the game's kick-off now means it will be open as Gregor Townsend's men look for their first win in Cardiff for 22 years.
Saturday's forecast is for persistent light rain and it is expected that both teams will have their captain's runs under the roof, Wales having already done so.
It is an interesting change of decision from Scotland coach Townsend, who on Thursday spoke about how he would prefer the Principality Stadium roof to be open.
"I looked at the forecast and it looked quite nice. I would much prefer playing with the roof open if we can," he said after announcing his team for Saturday.
"It is noisier when the roof is closed, that's why they (Wales) are disappointed. They don't get that (advantage)."
That initial decision from Scotland frustrated Wales head coach Warren Gatland, who feels there should be a change in the regulations to give them the power.
"We always want the roof closed," he said on Thursday.
"I have been consistent in terms of that. I just think it creates an unbelievable atmosphere.
"The thing about the roof is that both teams have to agree. I look at it and say 'well, it's our stadium, we should be able to say whether it is open or closed'."
He added at his team announcement: "The roof's going to be open, Scotland want the roof open which I think is a little bit disappointing from an atmosphere point of view, because when that roof is shut it does tend to create a lot more atmosphere and noise in the stadium. But that's the decision that they made."