@Dean1gsheheyw 

Hey

OK so the 110 wont work with Mesh regardless of the 225 being there, you need all your APs to be capable of Mesh for this to function for you. 

In short, the AP on your roof is going to be the ROOT AP, the one in the barn the 1st Mesh AP, however as said this wont work with a 110 in there.  You could swop out the 110 for a second 225 and have 225 to 225 Mesh, that would work but its not the perfect scenario for you.    These APs are designed to serve clients in a short range, this isnt their ideal setup.

Assuming you only want to send the signal across to the barn, basically a Wireless Cable for descriptive purposes... As mentioned earlier another solution is the CPE range, these are what are known as PtP connections (point to point).   You could return the 225 and OC200, get 2x CPE210 or 510  and mount them facing each other, they have a range of KMs not meters

Connect one to your Switch in the house and mount it outside.  Mount the other one on the barn and cabled into a cheap switch (better) or straight to camera (personally would avoid straight to camera).   Setup the 2x CPEs at each end to see eachother and that's you. Basically, they are a wireless version of running a cable..  you need two of these to create a two way connection, seen people buy just one and try it.  The reciever will see the CPE, but wont be strong enough to reply to it, hence the other CPE is required

However..  bear in mind these are PtP so wont offer WiFi to other devices, they literally just beam a signal A to B..  If you want WiFi at the barn side you will need another AP to do this.   However as you have only mentioned a camera, this may not be necessary...

Hope that helps!!

2x  225s in Mesh with OC200 has the advantage of offering complete WiFi in the area of Barn and House, range however its at its limit..

CPE will handle the range without breaking sweat, but its not capable of serving clients in that setup.. its just a way to span the distance.

  @Philbert would I still need 2 if the cameras are wifi enabled and in direct line of sight of the cpe 210 or 510

  @Dean1gsheheyw 

100% you would, its simply a matter of distance

The CPE on your roof would fire 10db to the barn and the camera there would pick it up OK, however when it tries to reply it cant do 10db signal back over the distance, therefore you need the 2nd CPE to do the sending. 

I had a customer do the exact same thing for a laptop in his summer house (~100 meters)..  CPE on main house blasting to the summer house, laptop in summer house read PERFECT signal but when it went to reply, the signal being sent from the laptop was so weak that it corrupted on route, the CPE did see it (barely) but it was garbage.. checked logs on the CPE and Transmit errors none.. recieve errors 99%...   He setup the second CPE at the summer house, worked for years now. 

Both send and recieve need to be working for WiFi to operate successfully.

  @Philbert which is the best one to have the 210, 510, 605 or the 710

  @Dean1gsheheyw 

The 210 is likely the cheapest as its 2.4ghz, the 510 is a bit newer and 5ghz.   Either of those should be good enough for you, anything else is just unnecessary expense.

IMHO I would go 510, unless budget is a real consideration in what case 210 is likely fine also.  Both do 5km range so 100meters is childs play.

  @Philbert I've just plugged in and positioned the two 510s and tried to log in to the page that the instructions tell me 192.168.0.254 but nothing is coming up is there an app or am I doing something wrong as usual 

  @Dean1gsheheyw I've now managed to log in and im at the setup page, what's the best option bering in mind I've got 2 510s so ones connected to my router and the other one is at the barn, access point, client, repeater, Bridge, ap router

  @Dean1gsheheyw 

Hey

Usually you create one as an AP and one as a Client, i would go Home for AP.. Barn Client

Go to youtube and look for   TP-Link PharOS CPE Point to Point Configuration Easy step by step (CPE610 | CPE510 | CPE210)     That video should get you going, its pretty comprehensive..

  @Philbert OK I'll try that in the morning, I bet you'll be glad to hear the last of my wifi problems. Thank you for all the help 

  @Dean1gsheheyw 

You are more than welcome!