The Rotoship was flown over to the Lam Building by one of Lam's soldiers in order to provide backup in killing the ones attempting to kidnap Wee Ming Lam.
The Rotoship is built like a cross between a jet and a helicopter, but more maneuverable than either. It has three rocket boosters on its back and navigation lights at its front. It holds turrets at its front that spray multiple bullets at once and has rocket launchers on its wings.
When the Rotoship first appears, have Glas quickly run to the exposed ladder and climb it before the rotoship pad blows apart with him on it. When he reaches the guard post, climb the ladder to the top but don't climb onto the roof. Wait for the Rotoship to appear and fire at the top of the guard post before flying off screen. Just as it does this, pull Glas to the roof and immediately run across it and hurry down the other ladder before Glas gets shot by the reappearing Rotoship.Once on the roof where the Rotoship's health meter appears, run all the way to the left and hug its wall behind the banners. When the Rotoship flies behind the banners and the target icon appears, fire away to shoot the banners into the Rotoship's engine. Repeat the process by running all the way to the right and shooting the banners there when the target icon appears in order to have them get sucked into the Rotoship's other engine. This will destroy the Rotoship for good.