how do build a paintball coarse, tips?

Yeah anything works.

Hek! You could buy hay bales and stack up 2 or 3 and then put a wooden stake or 2 through it to hold it to the ground.

Is this field going to be permanent? Are you going to let others use it? Is it on private or public property, do you or your family/friends own the property?

Safety is the most important thing in any paintball field.

Go over your prospective field and look for hazards try to remove all metal and broken glass that may be in the field if any.

I would recommend not using glass on a paintball field too great a chance of injury. Plexiglas and Lexan would probably be ok to use.

Make up signs that warn possible spectators like “Warning Paintball field ahead no person beyond this point without eye protection.”  About 70 yards after those signs have a sign that on one side says “Barrel plugs / Barrel sleeves can be removed at this point.” On the other side of the side have the sign say “No marker without Barrel Plugs or Barrel Sleeves beyond this point”

Those election signs would make a good holders for the above signs there easy to stick in the ground and you can hang just about anything you want on them.

As mentioned above anything that can stop paint can be made into a bunker. Your options are almost endless.

These next two items are great to have and never need.

If you can get a small first aid kit to bring with you to your field they are good for cleaning up minor scrapes and cuts help prevent infection

A cell phone or another reliable means of communication in case an ambulance is needed.

 The last thing you need for your field is some friends and have a good time.