Hello Everyone ! I just joined this community and I am eager to build my own 3D printer. But I Need help to know where to start.
Thank you very much !!!
What is your budget ? How technical are you (assembly, soldering) ?
http://reprap.org/wiki/Build_A_RepRap
Ask around before purchasing kits. There are a couple bad eggs out there, and new vendors all the time.
No specific budget. I am a student in electronic/computer science school, and I have enough the knowledge to build the structure, I just miss the knowledge for the 3D printing itself : plastic extruder , where to find it etc… Thanks for your help 
I am trying to have feedback on material, I am planning to use an arduino and controle motors, but I would like to know the best combinations
I would start with a budget first, that will dictate your first one. Then go from there.
Truely reading the rep rap wiki has everything you are looking for. Extruder design, material info, extruder typical temps, etc.
Building a printer is like buying a car, there is no “best printer for everyone”.
Do some research, there is tons of info out there. Several print methods (resin based solutions, filament based solutions, and powder based solutions). Several structural designs, several positioner designs, different motor controllers for each solution. On top of that there are several kits.
Before you get overwhelmed, with options you need to decide several things:
Do you have more time/ money?(if you have more time Thisbuy a kit with acceptable resolution, you will probably save money due to shipping and sourcing, if time is the issue buy an assembled printer, if neither is an issue: design and build it yourself it will probably cost more then a kit and take a long time)
What are you wanting to print primarily?(this will tell you what type of materials you can use ,what resolution you need, and most importantly print volume)
What is your budget?(there are printers in every price bracket from $200 to 200k and even higher depending on needs)
What is an acceptable cost per print?(abs and pla are pretty cheap now thanks to rep rap, but the quality of the rosin prints are astounding)
How much space can you devote to printing?(that is storing materials, printer volume etc)
Before anyone can answer you question you have to decide on those key questions, it would be ill service for anyone to make those decisions for you. I recently made a decision on buying my first printer, actually it has not arrived yet, but I can tell you why I chose my printer, and what apparent short comings it has.
Thank you everyone for the help I’ll keep you up to date When I start my build 
Do you have physical resources to help you with the build? A Hackerspace, Makerspace, School?
Basically, I already have a structure in mind, and the material to build one, I have my motors and I still have to figure out if I’m going to control them with an Arduino, or make my one controller using a PIC. I just have no idea where to find a good extruder.
Alexandre, basically everything you described is in the wiki. Please try to read it.
I will of course