How do you intend to add z info? One option is to create a vector of the same length as x (or y) using the ones or zeros function (your shape will still be flat but will be viewable as a 3D object). e.g.
z = zeros(size(x,1),1); % shape centred at z = 1
z = ones(size(x,1),1); % shape centred at z = 0
you can add noise too
z = zeros(size(x,1),1)+rand(size(x,1),1); % add noise
Besides this I'm not sure how you will arbitrarily add 3D info to your 2D shape
