Step 1: assemble the main frame. This is the four verticals (gold 2x2s), the ceiling bars (blue 2x2s), and the horizontal floor side bars (blue 2x4s, also via Kedreeva's design). And the bottom tray's poop tray support which is identical to the ceiling bars.

Step 2: attach 4 additional ceiling jousts (dark blue 1x2s). There are eight of these, but we're just putting 4 on for now. These are deliberately a bit off center, in this case they are placed so that the left side is 1/8 inch right of center.

This is so that I can do step 3: Cut these holes in a piece of 1/4 inch plywood and attach it to the blue jousts. This will be a little bit tricky to get into place due to the funky holes, but I think that if I put it down through the top at an angle, and then straighten it out front to back, it'll work. It is now centered in the frame.

Step 4: put the other four ceiling jousts on the other side of the plywood. Now it is sandwiched in place, and all the ceilings have a frame on all four sides to staple the wire down onto. Probably do that now. (Or for extra overkill put a plywood top on, but I have elected to leave the ceilings between tiers as wire. They will be mostly covered by the poop trays, and what opening is left will allow for ventilation. The topmost ceiling should be plywood, however. It is omitted in these images for visibility of the interior.)

Step 5: Build the floor frames (orange 1x2s), including two pieces of coated wire mesh on the bottom. Three of them. I could have done six individual floors, but I thought it would be stronger to have a shared back beam across both. Stick these into the frame from the back, top of the back bar level with the tops of the side bars, top of the bottom bar two inches lower. Attach via screws into side bars and plywood partition.

Step 6: Attach the back and left wall (brown plywood). The way I have it measured, attach the back first, then the left wall.

Step 7: create six doors (purple 1x2s, purple plywood), three backed with plywood and three with wire mesh. Attach these to the verticals with hinges on the sides, and also put in latches of your preferred type.

Step 8: insert poop trays (grey)

Step 9: Attach plywood (orange) to the bottom of the rollout trays. This will be under the wire, and has the benefit of further stabilizing the trays in addition to protecting from drafts.

Step 10: attach tray doors (brown plywood) to the sheet attached in step 9 with hinges. They open upward to remove the poop trays. Probably install a latch to hold them in the open position so you can have both hands. These could honestly have only gone halfway across since the right side doesn't need draft protection, but I felt like putting them all the way across. Might change that later.

Step 11: attach egg tray lid (greenish gray plywood). This hinges to the front of the egg tray, and DOES need to go across the whole way because it is protection from predators as well as from drafts. Include latches. Might swap it to a thicker board later, haven't decided yet.