are you talking about from absolute scratch? there's a program called G thang
that lets you choose from a number of popular guitar designs, and even lets you alter them with a little practice.

you can buy acrylic guitar templates at a number of places


and here's more plans

you can also buy some guitar making booksnthat come with plans inside the books.

if you're not planning to make the guitar from scratch, you can use the lmi kit wizard to assemble everything you need to make a guitar in any wood, size, etc. you will need an account to use it, but it's really cool! http://www.lmii.com/CartTwo/GuitarKitWelcome.asp
Quote by Skeet UK
I just looked in my Oxford English Dictionary and under "Acoustic Guitar", there was your Avatar and an email address!
I've purchased plans in the past from a number of places, but have been most impressed by the plans from Georgia Luthier Supply - [forbidden link].

I think they are a pretty small outfit, but their plans are extremely detailed and very accurate. Hope this helps!