Hi mark

Do you want to wired connect the two 5210G to main router's LAN port and cover Wi-Fi signal inside and outside the building?
If so, configure both 5210G in AP mode, one in channel 1 and another in channel 6/11.
But noticed:
1. User inside building may get poor signal strength because of the preventionof walls.
2. Configre 5210G as main AP is not a good choice since it's a 11g product. It will force the whole network to run under 802.11g mode which may lead to low transmission speed.

If not, provide a clear demand and tell us more information, height and distance of each building, etc.

Thank you for your reply.

Inside the buildings is not an issue

First i thought i would use them piont to piont but could not power a router the other end of the site so the router internet supply is only in the office

We have a N model on the roof of the office already but the trees stop the signal so I purchased 2 G models so i could place one either side of the trees which then gives a clear line of site for every one . p.s its a small campsite

I know the ideal option would be piont to piont and have a router connecting the secound one up the top of the campsite but with no power up that end my options are small, the distance from the office to the top of the campsite is about 200 - 300 metres each side the hight of the buildings arnt really an issue as ive got access to poles.

I had one thought about tapping into the campsite power pionts at the top of the campsite and placing a router in a waterproof enclosure then configuring them piont to piont.... your thoughts

mark

So you got a 7210N on the roof of office and two 5210G: one in building_1 and the other in building_2. You want to cover outdoor area around the two building, right?
But you can power one device in each place for lack of power appliance.
If I get the correct demand, the best solution may be P2mP application.
1. Wired connect the 7210N to the router's LAN port in your office, DHCP disable.
2. Configure the 7210N in AP mode, channel 1. Mount it up and adjust it to face the target direction. Be noticed that the horizontal antenna beamwidth of 7210N is 60 degree, it might be very difficult for you to cover the both position. And this is based on your real scenario.
3. Setup the two 5210G in Bridge with AP mode(Point to Multi-Point), one in channel 6 and the other in channel 11, DHCP disable.

Line of site clearance between 7210N and two 5210G is not enough, but a 1st Fresnel zone. Refer to the link below:
http://www.tplink.com/en/faq-907.html