Its like asking how long is a bit of string regarding a decent spec. A decent spec for what? All round use such as word processing internet etc, or gaming, or digital photos, ot video editing etc etc.
Regarding books theres loads but which is best I'm unsure, part of the problem is things move on so quick. You'd be better seeing what your library can get you rather than buying something that would be out of date in a couple of years. Also it does cost more now to build a PC from scratch unless you've already got a load of the components.