Design
Materials
Building your own display units is cheap in material costs, but expensive in time. Materials such as plywood, hardboard and chipboard (which must all be battened) are cheap and versatile. They can be painted with emulsion (but remember to prime them first, or they will swallow the paint) or covered with hessian or looped nylon.
Doors are very useful. Three flush doors, which can be bought very cheaply, can be painted or covered and then hinged together to make a very versatile display system.
Sheets of perspex or oroglas are also very useful materials, but they are more difficult to work with and rather more expensive.
But remember the basic disadvantage of most home-made display systems: they are heavy and difficult to transport, and usually look home-made.