[be] rolling in (it|money)

to have a great deal of money

The phrase "rolling in it" is an informal expression that likely originated in the United States in the 19th or early 20th century. This idiom is used to describe someone who is extremely wealthy or has an excessive amount of money.

After his successful business venture, he is rolling in it, buying expensive cars and luxurious properties.
During the economic boom, many entrepreneurs were rolling in money, making substantial profits.
If the startup takes off, they could be rolling in it in a few years.
The lottery winner was rolling in it, enjoying a life of luxury and indulgence.
With the new contract, the company is rolling in money, expanding rapidly.