I have needed a heavy duty crane for a while. So last week I decided to build a hydraulic gantry crane. I shot several videos of the crane in use, being built, and the design planning.
Disclaimer: Lifting heavy objects is very dangerous. If you are not confident in your welding and fabrication and design abilities please don't do it. Lifting thousands of pounds can create a situation which could cause serious personal injury or death.
Now that you have been warned, this crane is designed for 5,000 pounds but could probably handle 9,000 based on the beam strength from an engineering calculator.
I used inexpensive, off the shelf hydraulic rams from Harbor Freight ($30/ea on sale). About $450 worth of steel and $80 of wheels from Northern Tool.
The wheels are mainly to make it easy to move on rough surfaces.... you could adjust the wheels to be smaller or to be on parts that flex and remove the load when you lift. The wheels are rated for 1,000 pounds each but I found on a smooth surface I'm able to move the crane loaded which is a huge bonus for me.
One of the videos showing it in use:
Playlist of all DIY Gantry crane related videos: