I have a decked balcony and was wondering if anyone knows if I can lay turf /grass on it and if so any tips. Also have a rabbit so needs to be rabbit friendly!!

Generally, no. If it's wood, it would eventually rot the entire thing away. And even if it's cement, you would not be able to get the right drainage. There are other factors too, but in short: very impractical even if money is not an issue.

Nowadays they make some excellent outdoor carpeting. Check these couple links:

Astroturf,Artificial Grass,synthetic lawn,sport surface,fake grass,plastic turf,UK (http://www.kccarpets.co.uk/)

outdoor carpet astroturf - Google Search (http://www.google.com/search?hl=en&q=outdoor+carpet+astroturf&btnG=Google+Search)