I live in a first floor flat, and have no garden - but do have a small gravel area out the front, which was where our pup weeed and pooed until he was allowed out. It worked really well. Obviously I picked up the poos (there's a dog poo bin across the road, which is handy) and the wees drained into the gravel. He ended up doing each in a specific part of the gravel (wees just outside the door, poos next to the bins!). Once he was let out he also established his preferred areas - wees in the gutter outside and poos in the gutter across the road (unless we're going to the park, in which case he holds it in!). Not having a garden was initially a concern, but in fact it's made it so much easier! He was house-trained really quickly - got the notion of going out of the door and doing his stuff outside (it was the summer and I took him out ALL the time!). I used key words to encourage him ("weeeee!" and "poop!" and he now kind of wees on command, if he needs to go). I wouldn't leave the door open (not really an issue at this time of year!), so she learns that she has to ask you to go out (by sitting at the door and whining, for example).
I think you'll be fine using your patio. It probably rains enough to drain away the wee - otherwise just hose it down from time to time. Henry's wee does stain the tarmac on the road, until it rains. If you had grass you'd end up having burnt patches from the dog's wee anyway.
Looking forward to piccies!
