It's usually preferable to let your dog relieve herself outside. Of course, circumstances like living on the 18th floor of your highrise might make frequent trips outside a bit impractical, especially during potty training or with a dog who has mobility problems or difficulty controlling her bladder or bowel movements. Creating a potty area on your balcony for your dog might be a good solution; it's conveniently located nearby, yet you don't have to coexist indoors with the smells of your pet's leavings.
Choose one exact spot for your dog's bathroom on the balcony. An established and consistent location is key to potty training. It's probably best to keep the toilet away from the edges, in case your dog overshoots her target; you don't want to be responsible for unpleasant surprises on people below.
Place a litter box that's large enough for your dog to climb into on the potty spot on your balcony. Fill it with dog litter, which is made using larger pieces than cat litter to reduce tracking and to absorb more urine, since dogs pee more than cats. Another option is to use turf or sod pads, which you can also place into a litter box to help prevent spillover or misses.
Keep other strong scents away from the potty area, because your dog first learns to identify it by the smells of her previous leavings. So if you have a small grill, ashtray or other items giving off potent odors on your balcony, relocate them as far away from the potty area as possible.
Train your dog to use the potty area by leading her there by leash when she has to go. Offer immediate positive reinforcement when she uses the potty in the forms of a treat, praise and physical affection. When first potty training, bring your pet to the potty hourly, after eating or drinking, before and after confinement, after active play and before and after sleep. Learn her signs that she needs to go -- they may include circling, sniffing the ground, whining or scratching at a door -- and watch carefully so you get her to the potty on time.