The phrase "a massive build up" is correct and usable in written English.
It can be used to describe a significant accumulation or increase of something, often in a context where tension or anticipation is involved.
Example: "There was a massive build up of excitement leading up to the concert, with fans eagerly awaiting the band's arrival."
Alternatives: "a significant accumulation" or "a substantial increase".
Intelligence reports amassed throughout the years of negotiations indicated a massive build up of conventional weapons in the demilitarised zone along the South Korean border targeting the capital Seoul, but nothing was done.
He added: "There have been various reasons, not least the two Champions League finals at Wembley Stadium, which have been fantastic occasions and required huge resources and a massive build up time behind the scenes".
The following decades saw a massive build-up of shipbuilding at this historic Medway dockyard.
Several agricultural practices, including the use of seedbed nurseries, have also contributed to a massive build-up of RYMV inoculum.
During the "Cold War" (1950s to 1980s), there was a massive build-up of nuclear armaments, particularly by the United States and the Soviet Union.
As we know, what happened in practice was that the euro, combined with financial deregulation, allowed a massive build-up of debt in the south.
"The whole Star Wars mentality has the potential of swamping NASA," said Senator Riegle, especially when the value and place of a civilian space program deployment would require a massive build-up of launching capacity from both shuttles and conventional rockets.
"The two Scotland-England games I've been involved in had a massive build-up and a massive emotional experience.
The adaptive modeling of endosseous implants, as a response to load, is a massive build-up of immature buttress-like skeleton which then decrease externally as the interior layers become more mature [28].
One is a massive build-up of government bureaucracy.
Even its capacity to engage in a series of disasters over such an expanse of the planet for twelve and a half years and still be talking about "pivoting" militarily to Asia, while maintaining a massive build-up of U.S. forces around Iran, should give anyone pause.
