This was done in 2x6 framing lumber and sheetrock (the sheetrock has to attach to something....)
They were sheet-rocked with radius edge corners.
SInce it is built on site - its up to whoever is doing the work to price it for you - labor costs vary greatly.
To repeat a previous posting:
The ceiling here is 9' high and the width of the hallway is 5'9" wide. Assymetry was key here, but some order was maintained with 3 equal width divisions at the top. A good way for you to tackle it is to cut out large squares of paper/cardboard and tape them up to see the effect. Make sure there is room for any particular pieces of art you would like to display.
Check with your electrician for which lights can be installed and how deep a recess you would need (codes vary).