Oak WILL look different than ash, unless it is completely drowned in dark stain so that one cannot see the grain (essentially like painting it). If you have a digital camera, send me a well lit photo or two and I could tell you if you cabinet is oak or ash.
When you stain and poly this thing, I would highly recommend applying the same amount of stain and poly to the INSIDE of the canopy as the outside. Some people ignore the inside because no one will see it and, believe me, they pay the price. The canopy will be firewood in a few months. (I apologize if you already know the fundamentals of working wood. I figured better to say something than not to...).
As far as the 1/2 inch oak/ash weight. Your question depends solely on the canopy design. For the most part, 1/2 inch stock would be exactly what I would use. I have built many for the clients of my local LFS who buy 300 gal and up units for their offices/homes, etc.
Oh yeah, one last thing, I have used the Minwax Red Mahog stain. I would also bet that this is not the right stain (sorry, Mick!). But, different stains look different on different woods with different sanding techniques...they always come out a little different. If you want a close to perfect color match, you will need to test the stain on scrap wood that is prepped (sanded) the same way as your canopy, and then adjust it from there.
Good luck,
McReef
