How big should the chamber be? how long is a piece of string?
This question depends on how much power you want from your launcher, try using a brilliant free bit of software called
GGDT to estimate your power and performance and have a play around with it, although from what people have gone with before about 150-200 cubic cm should do you fine.
With regards to your valve, I wouldn't worry about it too much, pretty much anything that deposits air fairly quickly at a push of a button will work, have a deeper look into
exactly how they work and how to use them if you are still unsure,
As for existing examples, try out the
Showcase section of the site, there are plenty there to see, and some might even give you some extra ideas for your own build,
Also, probably worth mentioning, some folks here can get a bit annoyed when people double post, if you need to add something try the edit button, just thought I'd get in there before someone gives you some bad rep for it,
