are there any for understanding them? or any on how to build pedals?
Here's where you can buy a book on building pedals and also one about modifying them: http://www.smallbearelec.com/Categories.bok?category=Books+And+Publications (http://www.smallbearelec.com/Categories.bok?category=Books+And+Publications)
You can find out what some symbols mean in schematics in the DIY FAQ: http://www.diystompboxes.com/cnews/FAQ.html (http://www.diystompboxes.com/cnews/FAQ.html)
...and google has some links to articles and books you can buy : http://www.google.com/search?client=safari&rls=en&q=reading+schematics&ie=UTF-8&oe=UTF-8 (http://www.google.com/search?client=safari&rls=en&q=reading+schematics&ie=UTF-8&oe=UTF-8)