The bowl-shaped structure will serve as a public art depot for the Museum Boijmans van Beuningen. It is scheduled to open in 2021, but the building is on track to be completed later this year.
A topping out ceremony already took place in the Dutch city, in September 2019.
To reduce the building's impact on the park, MVRDV kept its footprint as small as possible, hence the bowl shape.
A sculpture garden is being added on the roof, to make up for the lost green space. Over the next two weeks, 75 birch trees are being installed on this roof.
"When Yves Brunier designed the Museumpark with OMA, I helped with the selection of the old trees," said Maas.
"Now that the birches are being placed on the roof of the depot, the circle is complete; we are taking the park we removed to the top of the depot and enlarging it," he continued.
"Soon, people will be able to take the express lift up, free of charge, and enjoy a spectacular view of the city at a height of 34 metres."
MVRDV won a competition to design the Depot Boijmans Van Beuningen in 2014. Billed as the first publicly accessible art depot in the world, it will allow the public to see how and where historic artworks are stored.
The building will contain enough storage for the museum's 151,000-piece collection, as well as exhibition halls and a restaurant.
The project has proved controversial, with critics arguing that its size overpowers the small park.
Depot Boijmans Van Beuningen is expected to open its doors to the public for the first time on 25 to 27 September 2020, while it is still empty.
It will then close for a year to allow artworks to be deposited inside.