Lay out the wall on the floor, making sure that the grid portions of all of them are the same side up. Secure with cable ties. Don't pull the cable ties fully tight just yet; leave a slight give to them (see photo below). You will tighten them later. Repeat to make the second wall.

Secure the grids together with cable ties as in step #1. Repeat to make the second side wall.
After you use the cable ties to connect the four walls together at each square grid, you will find that you can manipulate the cage to be various shapes, e.g. triangle, pentagon, etc. Decide on the shape that you want at this time. Mopsy chose a rectangle.
Slip two dowels through the grids along the length of the cage. The dowels will prevent the bun's shelves from falling through. Where you put them depends on the shelf layout and door location. Mopsy contemplated a larger lower level and high door, but ended up settling on the layout shown in step 9.
Place the plywood on top of the dowels. Bunny is optional at this stage.
You're almost done. If you want, take a moment to relax with a snack. Mopsy recommends the handle of a wicker basket.
Use the small spring to clasp the door shut. It's okay. Mopsy and Julius get along.
Mopsy likes a towel on each shelf, secured in place with clamps to help his footing. Mopsy says he really likes his new bunny condo, especially because it includes room service!