It is believed the accident happened as the workers were preparing a concrete pour on the site where a massive new water tank is being built.
One of the workers injured his back and had to be lifted out using a crane.
The injured men are believed to work for subcontractor Bell Formwork.
Costain is main contractor on the £15m project and has launched an investigation into the accident.
A West Midlands Ambulance Service spokesman said: “The builders were just about to pour concrete at the site when the accident happened.
“One man, who was in his 40s was treated for a bump to his head, but a second, who was in his fifties, had leg and back pain.
“Due to the location the only way to get him out was to use a crane at the site. The man was immobilised using a specialist stretcher.
“This patient and one of the HART Team paramedic were then lifted over 75 feet into the air from the location and then transported to the waiting ambulance by the crane on site.
“Both men were then taken to Queen Elizabeth Hospital Birmingham.”