This engine stand was made for the Daylight (4-8-4 Northern) while it was under construction.  It's 8 feet long and adjusts from 17" to 37" in height.  It doesn't allow you to adjust the height while the engine is on it but it is simple, cheap and doesn't take much time to build.  Angle iron is used for the rails but anything strong would do.  Five inch wheels are used in the drawing.  Any wheel size can be used as long as they can handle the weight of your locomotive. 

The three leg sections of pipe were "turned" on my lathe for a good fit. 

The top and bottom legs were then welded to the plates which were then bolted onto the rail and wheel sub-assemblies.  This allowed me to disassemble the stand for easy storage.  Here's a side view of the highest and lowest settings..

And a side view.