Always nice to see a home built. I made my own and know well the feeling of accomplishment it gives.
I have one question and three suggestions.
How long is the run of ducting, and how many bends? This can be more critical than the design of the booth. The run length and number of bends severely reduces the ability of the fan to move the air. See this tutorial for a more scientific explanation.
Now my suggestions:
- You should paint the inside of the booth white. I found that the wood coloring tended to mute the light. Painting it white (I used gloss "bathroom" paint) reflects the light and is brighter, and I can actually clean up small spills fairly easily. An alternative would be to line it with white poster paper which can be removed and replaced when it gets ugly.
- Typically backdraft or downdraft style booths have a plenum chamber to distribute the airflow evenly. This can be as simple as a piece of metal or fibreboard mounted a couple of inches in front of the fan.
- My final suggestion is to but some form of doors on it to keep the dust out while things are drying. This could be a easy as hanging a towel over the opening, or as complex as clear plexi doors.
Regardless, I know you'll be happy with your booth, and it will give you years of service!