Do you already have the routers? Are they all routers that can be set to AP only? You need one router connected to your modem, the rest should be AP only.
For wireless, set the SSID on all of them to be the same, and set them to different channels (1,6,11 which do not interfere with each other). Your clients should roam from one to another, but some clients are better at this than others. Also make sure security settings and passwords are the same on all APs also.
If you wanted something commercial grade, then you would want to set up a mesh network.