How can you train your dog to go in a certain area of the garden, our grass is being killed, so thought we could train her to go on the patio? She poops on the patio but wees on the grass...any tips???

Keep her on leash when you take her out, this way you will keep her in the same spot and also give a comand word like hurry up/go pee/be quick, lots of praise/treat. If you saturate your lawn down with water after she's pee's that should help :)

I have sectioned of a little area at the top of my garden for wees and poos. We put a little fence up so macey knows to go the other side of the fence.  I had to take her there everytime at first, in all weathers, it took a few months but now she always goes there.
I have to keep it clean though, pick up poo everyday, It's good because the rest of the lawn is fine, and no chance of the children stepping in anything.
She is 18 months now and I still praise her and give her a treat every now and then.

forgot to say, everytime I took her to the place at the top of the garden, I would be saying to her " up the Top,  do wee wees " now I just let her out and remind her, up the top.
hope this helps.