If you do not want to go the natural route you can of course make one as well.  The next best option would be to use wood but this can be difficult to make and if you wanted to go that route you could simply use trees.  You can also use plastic tubing.  Plastic tubing is very light weight. Initially it might not attract fish as quickly but over time as weed and other natural items grew onto the construction it will prove quite effective.
 
The one advantage of building an attractor as opposed to using a tree is that you can form the shape and size that you want.  When using a tree of course you are beholden to the size and shape of tree available.  You need to build a construction that has many branches that are not uniform. You do not symmetry; make your construction have a look of randomness to it.  Color is unimportant but size is very important.
 
Again when building the construction think about what you are doing.  Visualize what the underwater scene will look like after you have set it up.  Try to imagine how the Crappie will interact with your construction and determine reasons why your project will work.

To get the full "How To Build Crappie Fish Attractors" article you'll need to download it here.