The This Morning star gave fans a first look into the new room as she unveiled her decorating plans on her dedicated home Instagram account.
Standing in the L-shaped empty room – which features a corridor area opening up into a rectangle – Rochelle explained: "This room was completely plain and empty, painted that horrible colour that I hate – magnolia."
So far, Rochelle and Marvin have put in parquet flooring, moved plug sockets and added panelling across the walls and ceiling, with plans to finish it off with black and white paint. "This is all about to get painted today. We are going for a monochrome theme this time," she said.
WATCH: Rochelle Humes Unveils Her Daughters' Mindblowing Playroom
Speaking of her reasoning for moving the plugs, the doting mum-of-two said: "What I'm going to do this time is put a bed straight in from the get-go because otherwise, I find afterwards I think: 'Oh I need to put a bed somewhere.'"
The This Morning star showed off the new parquet flooring and panelled walls
Rochelle intends to put a bed against the back wall so the couple can stay with their son overnight if necessary, as well as a cot positioned to the right-hand side. On the opposite wall, the 31-year-old will create a built-in wardrobe positioned around an aircon unit, which will be boxed up and hidden apart from a grill.
"Today we start which is a good job because I've only got about three weeks left so don't turn up early please little man!" she joked.
Rochelle plans to surround the aircon unit with built-in wardrobes
Rochelle and Marvin's son will likely have a very different nursery to his two older sisters Alaia-Mai and Valentina. In their previous Essex home, Rochelle showed off Valle's neutral cream room, which featured a white round cot, eight framed photos of woodland animals, vintage-looking white storage trunks and a chandelier.
In June, the expectant mum wrote: "THROWBACK to my little Valle’s nursery...I designed this peaceful little room 3 and a half years ago with my very good friend @hesellicdesign. We had the most fun doing it and are currently doing it all over again planning a super cool room for our little man."