Attach two of the legs to the 1x4 foot board. You can either use pocket holes or pre drill and use 3” screws through the outside of the legs.

Attach the other two legs to the solid
Ladder wall. If using ph, make sure you drill the holes where your shelves and bench will go. This way they can be hidden.

Attach the side rails to the legs on either side.

Cut your desk top. For this step, take the 1x10 that you cut for your desk top and measure 1 3/4" on the long side (this will be the same measurement as the width of your 2x2 leg) Draw an angle from this mark to the opposite corner on the short side. I know this is confusing, so I included a photo of it.

Measure from the base of the back rail to the bottom of the leg. Cut a 2x2 to fit. I attached mine with ph from the top rail into the leg, and then from the under side of the desk.

Using glue and nails or hot glue, attach your steps to the ladder wall. I used a 1x4, between the steps, for a spacer.
I also mod podged a piece of fabric to a scrap piece of ¼” plywood for the back of the coat hanger. Then, I took 3 small cup hooks and attached them to it.

Then, attach your shelves to the inside of the ladder wall. Put your bench together with nails and glue and attach it to the ladder wall with ph screws from the top of the bench. Then, nail your slats to the side rails and cut a piece of 1/4" plywood or strong cardboard to fit under the mattress .Take the scrap plywood you cut for the desk wall and attach it to the back legs with glue and nails. I also cut a scrap piece of plywood and glued a piece of foam to it. Then, I covered it with fabric and some yarn to create a bulletin board for the desk.