I presume you have a townhouse or something similar so why would you want to "pave" over your garden area? Of course you could intermingle perennials between the breaks in the slate or you could put containers on top of the gravel, but don't you like the color green just grey? If grass doesn't grow, why would you want a grass patch of 20X25 to mow anyway? There are many things you can do, but I don't have any pictures except those on how to proagate perennials. Not the anser you are looking for but.

http://propagatingperennials.blogspot,com