They were from the 'disobey! direct action group and Preston Anarchists.
A UCLan spokesman said he believed they were protesting against research carried out by the university on behalf of BAE.
The leaflet given out also stated UCLan had money invested in the company through shares via a third-party fund manager.
Police arrived at the Foster building shortly after 1pm to remove the protestors from the roof.
Three people were arrested, were released and not charged; the university didn't want the media attention.
There is a video on local Lancashire Evening Post website.
This action called in solidarity to the people of Palestine, one of 19 campus protests across the country.