Looks good, but yes, you'll want some ventilation to get air around the coals. Might I suggest a perforated coals tray too, one that can be slid out to make disposing of the spend fuel a bit easier.
PS - Love Sketchup. I use it at work.
A good start, but a few possible refinements.
(Aint it a pain when people say 'Oh, how about this..... and offer dumbass advice)
Slidey thingy over the slots with corresponding slots in it so you can fanny about adjusting the airflow? Call it the Chunkulator.
Small extendable arm with hole in it to hold rehydration solutions. An essential item.
Thingumyjig to hang barbecuing tools from.
Chunko'.