I don't have the dimensions of this desk so I will pick my own. Most of these desks are slightly higher than they are wide. This one is going to be 40 W x 19 1/2 D x 42 H.
I started by making full size drawings of the desk. I'll make a story stick later from the drawings that I will use as I build the piece.
For the inside of the desk or gallery I am going to use an article by Lonnie Byrd from Fine Woodworking 2002 as a pattern. I really like how it looks.
The joinery around the lid and the quarter columns is a bit complicated so I decided to build a prototype.
I had some soft maple laying around the shop so I used it to build this small prototype. The depth of the prototype is 19 1/2 like the full size piece but the width is obviously narrower.
Here is where the joinery gets a little tricky. The quarter columns need a 1 1/4 inch recess, so to create it you cut back the side and the front. Then put a 45 degree miter on the writing surface. The vertical divider has a matching 45 miter to hide the joint.
This makes the first divider, you can see the 1 1/4 x 1 1/4 recess on the corner for the quarter column and second one would be tenoned to the right to create a space for the lopper or lid support.
Here is a sample of the quarter column.
Now the most complicated piece.
It has a turning of the capital for the quarter column and the balance of the 1 1/4 slope that is needed for the desk side.
It fits in here.
Here are the way they looked when glued together.
Then I placed it on the side and cut off the excess to match the slope of the desk.
There you have it. I think I now know how I am going to do the joinery. So I'll get started my making my story stick and milling the wood for the sides and top.