Welcome Tom, I'm just down the road from you, so to speak, in Vacaville.
A couple of things to keep in mind with risers and prosceniums. You want them to be as solid as possible. I used two 3/4" sheets of plywood on top, and I would conider that the bare minimum. Many people sandwich a 1/2" layer in between two 3/4" layers. Depending on the geometry of your room, 2 x 8 or 2 x 10 pressure treated lumber is a good bet for the riser framing. This gives you a finished height of anywhere between 9 1/2" and 11 1/2" which is about as high as you want to go, unless you want to add steps.
The areas between the framing joists should be, at a minimum, over-stuffed with insulation to deaden any resonances. Many people, including myself, filled the gaps with playground sand.
Overhang the plywood by about 2" for a nice lip and add 1/2 round to the edge for a nice finish. You can then run a row of rope lights underneath the overhang for a very professional looking finish. If you are going to use 120V rope lights, installing an outlet at one end of the riser is a good idea.
Cover the riser with some nice thick underpad and carpet and you're all set.
The proscenium stage should be of similar construction, although you may or may not want to carpet it. Usually the front speaker would rest on the proscenium stage, so again, solid is the key. The dimension are very much driven by the geometry of the room, projector, planned seating layout, etc.
In my case, I have a very narrow, high stage (16" deep, 24" high), for a very specific purpose. Since it is so high, I will probably not be filling it with sand, just stuffing it full of insulation.
If you can be a bit more specific about what you are looking for information-wise, we can probably provide better answers.