Step 3: Train trestles...
From a single piece of cardboard or pieces, make a channel type shape about 18 inches wide to enclose the ends of the upright legs.
You need four sets of trestles.
Sort out the legs to be even sized pairs. Glue on the cross piece.
You can use a level to check you are making an a level set of legs.
Place the level on top of your head. Check to see if your head is level.