A Faraday cage is an enclosure, room or entire building (like the NSA building at Ft Meade), encased in metal and then grounded to earth. It prevents electromagnetic waves from entering or leaving. It works the same as a coax cable (see picture) If the braided shielding is grounded to earth the conducting core is protected from noise coming from the outside. The NSA building is copper, but aluminum has the best reflective property's of any metal. Aluminum flashing can be bought at any construction supply (Home Depot, Lowes). Attach it to one side of some plywood panels and place the panels on the floor of the attic. Somehow ground it to earth. There are companies that sell and install metal roofs. This might defeat satellite surveillance but not cell phone towers. If a satellite can pick up EMI at 10,000 miles cell phone towers can do the same. Cell phone systems are on the ground and would be capable of snooping through the walls not the roof. To defeat this, the whole house would have to covered with aluminum. They used to sell aluminum siding, I don't know if they still do.

 
Coax Cable

A Faraday cage can protect from radiated intrusion, both transmitted and received, but it doesn't help with conducted surveillance. Any wire entering or leaving a building and connected to a utility (electric, cable, phone) is a highway for someone to snoop. Any house has thousands of feet of wire. A large building has miles and it can all be used for transferring data. Broadband Over Powerlines (BPL) is a technology that uses the AC wiring in a building for delivering the same data as the coax cable. Telephone wiring could also be used without a person's knowledge. It used to be that when a device was off it was off. But now almost everything plugged in is drawing current even when not in use. I used to think this was done just to pad the electric bill but it may also have a more sinister purpose. Anything plugged into a wall outlet in your house could be snooping. The wiring itself could be a problem. As a rule the bigger the antenna, the more sensitive it is. So the wiring in your house could be a very sensitive antenna capable of picking up your personal emissions. There are at least 2 ways to defeat some of these problems. Filtering and injecting noise onto the wires.

Some basic filtering solutions are snap on beads and inline filters. (see below) A snap on bead is a ferrite that can be placed on any wire to suppress high speed signals. Inline filters can be bought at home improvement stores and can be placed in series to filter out unwanted frequencies. The third picture is a filter that can be added to home built electronics.

 
Snap On Bead

 
DSL Filters

 
Inline Telephone Filter

 
Supply House Filter

Injecting noise onto AC wiring is basically the same concept as Broadband Over Powerlines. (BOP). It is possible to get a higher frequency signal to 'ride' on a lower frequency signal. X10 technology was invented in the 1980's. X10 uses AC wiring to control lights and other devices inside a home. The same technology could be used to put noise on the AC wiring.

 
X10 Controller Module

To prevent the AC wiring from picking up your emissions like an antenna you could place all the wiring in conduit or Romex conduit and ground it to earth. I know this makes no sense if your house has already been built but I'm just making a point. It's the same thing as coax cable. The conduit acts like a Faraday Cage and keeps noise from leaving the AC wiring or anything getting onto the wiring. Injecting noise onto the wiring is an alternative if you can't rewire everything. They make shielded AC wire but it's expensive.

 
ROMEX Conduit

I think it makes sense to both inject noise onto the wiring and filter it at the same time. Any device plugged in could be conducting surveillance. It could be using the AC wiring to communicate with the outside world. Generating noise inside the house could stop the device from picking anything up and injecting it onto the AC wiring can defeat it's transfer to the outside. Filtering at the same time can make sure.

Sidenote. Some people believe the HAARP facility in Alaska is used in mind control and surveillance. It's stated mission is communicating with submarines on Extremely Low Frequencies. (0 HZ to 100 HZ) In fact they think it operates around 30 HZ. It is possible to get high speed data to 'ride' on the 30 HZ. The 30 HZ might be powering the RFID chips and carrying the communication data.