I want to know this to see if I can do some modifications to my guitar tone but I don't want to screw the pickups...
is there any guide arround?
You certainly can, but I don't think you will get a great return on investment. Doing this well requires special equipment that people like you and me likely don't own or have the funds to purchase. If instead you are referring to wiring your pickups to the miscellaneous controls in the cavity and experimenting with unique switching configurations I recommend checking out the sites of guitar pickup gurus like Seymour Duncan, Jason Lollar, and Lindy Frailin. They all have wiring diagrams for stock and experimental wirings based on your pickup configuration. Another good informational site is maintained by a friend of mine named Deaf Eddie, and it's here. I learned a lot from him. My Telecaster is specially wired with a series pickup toggle switch, and thanks to Eddie I was able to figure out that I needed to install a certain capacitor somewhere in the circuit to tame the harsh, additive nature of a series pickup configuration. The results? Stellar tone with no volume bump and a more versatile Telecaster.
Also, if you are getting into wiring you're going to need to know some basic techniques and how to use a soldering iron, among other pieces of information. Stewart Macdonald has a decent informational archive on this, and a quick google search turned up a few FAQ's like this one.
Given that pickups used to be (and some maybe still are) created by hand, there's no reason you can't do it if you have the tools and knowledge of electronics to do so.
Of course winding what's essentially an electromagnet by hand is a tricky thing to do, it requires great precision.
Pickups are very simple instruments and are primarily characterized by their winding geometry, number of turns, and resistance. All the little screw-in terminals etc. do surprisingly little to the device (although I'm sure many guitarists will be at my throat for that).
The actual process of winding a pickup is as easy as it looks, you can either do it by hand (tedious and prone to error), or build a jig for it (I have seen plans online for it). As long as the windings are relatively uniform on the pickup you should be fine. Personally I just use a lathe and a roll of wire, turn the lathe on and use my finger to move the wire back and forth to evenly cover the pickup. You essentially wind until you achieve the resistance you are looking for.
Designing a pickup is a whole different issue. The geometry of the windings (i.e. single vs humbucking, split, etc.) is determined by your sound goal, the resistance is also determined by the sound you like and the application (i.e. active vs passive), very high resistance pickups are typically associated with active setups, "hot" passives are usually higher resistance passive pickups. The same resistance can be achieved with several different winding numbers (of different thickness wire), in turn the wire gauge you use (and the number of turns per DC resistance) determines subtle sound characteristics due to the extra capacitance of the extra windings. The magnet used for the base can also affect the sound characteristic, although you are getting into the same kind of territory as trying to argue which wood sounds better for an electric guitar.
If you want to get your feet wet, you can cannibalize an existing pickup (broken, cheap, or otherwise) and try winding it, replicating the wire gauge and resistance readings. Once you get the hang of it, try playing around with the # of turns/wire gauge/ etc. to see what sounds better for you.
Basically, no harm in trying it out so just go for it.
I build cigar-box guitars, and a number of builders who frequent the clearing-house site Cigar Box Nation: http://www.cigarboxnation.com/
make their own and even offer them commercially. The proper wire is not cheap, but it's readily available. An average pickup requires thousands of windings, and a single break in the very fine wire means you start all over again.. Most makers build or improvise a winding jig of some sort; old sewing machines are popular.
It's hardly worthwhile if you just want one or two for a project, though it might be satisfying. However, if you were planning to do a number...
As far as I know a lot of pickups are still made my hand but the creation is still aided with specialist tools you'll need to get your hands on first. In all honesty, it won't work out cheaper than going out and buying yourself a nice set of new pickups, but if you're doing it for the "I made this factor", then you definitely can.
This book is one you can't go past if you want technical specifications on pickups and info on building them yourself, it'll teach you everything you want to know and more.
I just found this instructions page to make your own pickup... It will be almost free, but I would not expect much of the sound quality... Interesting project though.
Pickups can be wired by hand and StewMac / other places sell kits to make pickups. I myself bought some wire, and magnets off K&J magnetics to make a pickup but haven't got around to it yet. A possible problem you could run in to is if your guitar has active pickups (uses a battery), then the process changes.
If your goal is to get new sounds out of your guitar, first try raising or lowering the existing pickups. I have found this to create much more dramatic changes in tone compared to pickup replacement with different flavors of the same design (different strat single coils, for example).
If you want to build your own pickups for the fun of it, go for it! Your worst case scenario is that you fail miserably and learn something in the process.