Stronghold Crusader HD: How to Build Siege Equipment
In order to get your siege engines up and running, you need engineers to build and man them. With an engineer selected, click on the siege equipment button to see a list of machines that are available to build. Select the piece of siege equipment you wish to build then left click on the map and a siege tent will appear. Selecting this tent will give you an idea of how long the equipment will take to build. Siege tents are easy to demolish and the engineers inside are vulnerable until the equipment is finished so ensure you protect them well.
All siege engines need to be manned. To do this, select a group of engineers then move your cursor over the piece of siege equipment you wish to man. When the cursor turns into a down arrow, left click and the engineers will move to the equipment and man it. Different types of siege equipment require different amounts of engineers to man them before they become operational.