I need to transfer maybe something like 2-3Kb/30sec... through 20 meters but through 3-4 walls... 
So, I don't need/want WiFi module, but I need a middle-high power signal and all of this can't eat too much energy...
Maybe you have an idea ?
I thinked about 433-315Mhz, but I don't know specs about that technology...
@mfalkvidd .
Thank you for your help! You are really useful!
I will try somewhere else.
Thank you for your answers! 
My questions were calling your experience. Of course I'm able to read a tutorial and I'm sure MySensors's bloggers are really able to write some topics about it!
But I'm looking for someone who already did it and build all of this alone, without manufactured products ready-to-use.
Because that person is able to say me, "Pay attention, if you have.....", "I advise you to make more like that.......". 
And too because like that, I will have someone who can say me, "I tried that but it gave bad results. Maybe you should more use......"
Hi everybody!
I'm a student and my english is not my greatest pride!
I have a lot of questions without, after so much hours Googling...., real answers!
I'm trying to build a full domotic network at home, with PiDome. (I'm sure you know it! )
My project is to connect multiple ATmega328P wirelessly to Raspberry (working on Linux distribution, with PiDome server).
I have a lot of problems, maybe you can help me!
I want to know how to connect a ATmega328 to my RBPi
-->how....? (Wifi Module, 433Mhz, etc...) (considering the factor walls, and others...) -
--> and that I want to make that as secure as possible (maybe : avoid WiFi ? I don't know...)
How to interface between ATmega328 and RBPi, considering I need to give orders from RBPi to ATmega and I need to send datas from ATmega to RBPi...
--> Is it possible to make that easier with MySensors ? (Code side)
Thank you all for your help!
Ps : every components should be cheap! Of course 