@Cheflatho 

There are a couple of options to extrend your Deco Mesh Wi-Fi to an Out-building.  

First thing you need to do is insatall an App on your Smart Phone.  I recommend "Wifi Analyzer" by Kevin Yuan.

- Run the Wifi Analyzer and test the signal strength of your Deco which is closest to the out-building. The signal strength is from strongest (-20dBm) to weakest (-100dBm). 

- Check 2.4GHz and 5GHz (tap the upper left above -30, to switch frequencies) You will need to test from your house and out to the out-building.

-  You will need to have a signal strength of no less than -55dBm at the location in the out-building where you will locate  another Deco Node. 

If your signal is better than -55dBm (meaning between -30dBm and -50dBm), congrats and you can just choose another Deco node and add it to your Mesh. Maybe a Deco M5 if you need Ethernet conectivity in the out-building.

If however the signal is weaker/poorer than -55dBm then you have two options remaining:

#1 if the Out-building's electrical is on the same side of your home electrical panel , you can use a TP-Link AV1000 Powerline Ethernet Adapter (TL-PA7017P KIT). This allows you to connect a wired Ethernet cable from your main Deco Router or network switch, to one Powerline adapter and plug it into an electric outlet in your house.  The second powerline adapter (they are sold in a kit 2-pack) will plug into an electric outlet in the out-building and an Ethernet cable will connect a new Deco node to the Powerline adapter.  Thus adding to your Deco Mesh. 

#2 Lastly, if the out-building is not on the same side of your electric panel, then you can use a Point to Point Bridge to extend the Wi-Fi from your home to the out-building. This is much more complicated, but works flawlessly.  Use a TP-Link N300 Long Range Outdoor CPE for PtP and PtMP Transmission, available in 2.4GHz or 5GHz. You will beed two. One to connect at the house and another on the out-building. You will need to have an uninterupted line of sight between the two buildings. The signal range can be as little as 20ft up to 1Kilometer.