Joanna Gaines has "really been having fun with picking out details like colors and bedding and the crib," Chip Gaines says of his pregnant wife

Joanna and Chip Gaines may not be quite finished with their fifth child‘s nursery, but they’re getting there.

Chip recently spoke to Country Living about the design process behind the room for their son on the way, insisting “it’ll be the most beautiful room in the whole house” when they’re finished.

“Jo is still trying to decide if she wants to hang some of her wallpaper on the walls and what kind of rocker she wants,” he says of his wife and Fixer Upper costar.

Adds the soon-to-be father of five, “We’re still right in the middle of it all, but I have no doubt that when Jo gets finished with it, it’ll be the most beautiful room in the whole house.”

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Credit: Joanna Gaines/Twitter

Chip and Joanna Gaines

The secret ingredient Chip, 43, started with in building the nursery? “A fresh coat of paint was first on the to-do list and that really does make all the difference,” he says, adding that Joanna “had a ball working on” the space.

“It’s been eight years since we’ve done a nursery for ourselves, and she’s really been having fun with picking out details like colors and bedding and the crib,” explains Chip, who shares sons Duke, 9, and Drake, 13, plus daughters Emmie Kay, 8, and Ella Rose, 11, with his wife.

RELATED VIDEO: Inside the Moment Joanna Gaines Found Out She Was Pregnant with Baby No. 5: “My Jaw Dropped”

Chip and Joanna, 40, recently opened up in a PEOPLE cover story about their expanding household, including how they split parenting duties.

“Chip is the best swaddler,” said Joanna. “He’s always been able to rock our babies to sleep. He’s like, ‘I’m going to be holding the baby the entire time!’ ”

Of diapering, she added, “We need to figure that one out again. I don’t even remember, but I do remember the blowouts and I’m like, ‘Oh my gosh!’ I’ve gotta get my stuff together. It’s coming!”