Fireplaces, Heating Stoves, Flues and Chimneys - construction and code ?'s

My plan is to construct a corner fireplace in our walkout family room. The room is unfinished as of now. The corner I planned to put in is on an outside wall, however it is a screened in area. One place told me I couldn't vent there, and another one said it was alright (just away from deck 18").
First, is a vent ok there?
Second, where can I find some info on constructing this thing, plans etc?

By the way it will be a gas fireplace.

I know I should just call my inspector, but it is a real pain trying to reach him, as he is only available 1 hr each morning which conflicts with my work schedule. Not only that, I feel like I am needing to ask about every little thing.
I wish the codes were online somewhere. :)

You could ask the folks in the permit office which code applies and pursue it that way. You can likely find the code on line. Locally, there may be some differences.

If you go to www.lennoxhearthproducts, click on fireplaces then click on gas direct vent fireplaces. From there you can download the installation manual from any DV model. In the manual you will find the code requirements for the vent cap as it relates to it's location next to windows and porches overhangs,etc... This is the standard code no matter the brand of fireplaces.

Hope this helps.