If you have a Precision exercise pen, doesn't matter what the hight, and you buy one of the size of 24 inches in hight, you can take apart the 24 inch pen- so that you have two segments consisting of 2 panels. Then if you zip tie the two segments together so they form a square of 4 segments, you can then zip tie this 'roof' to the top of your original x-pen when it is in the shape of a square- you will leave one segment free of zip ties to be used as a 'door'. Once you have completed zip-tying, remember to cut off the hanging bits. You can use the fasteners that came with the x-pen to lock the 'door' when you leave the dog alone.
If your dog is not yet house trained you can try this method of preparing the base of the crate, this particular method is for a dog that doesn't like chewing and tugging. For a dog that might eat the base, you could use a piece of linoleum. AND for dogs that are strong and learn how to lift the crates up and squeeze uder, you can create a secure base in the same way you created the roof- making sure to line it so the dogs feet aren't on the metal grate. You can buy tops to the pens, but they are 50$ a cover, and the medium size 24 inch pen is 63$- which you can make 2 tops (or a top and a bottom from), so is a better deal.
If you need to leave your puppy in a safe environment but are unable to return to let the puppy out to use the bathroom, you can put a square of grass sod in one corner of the pen (preferably in front of the door, as that is were they will be most likely to go, bed to the back), or a pee pad in a litter box. Grass is way better to use than pee pads as pee pads can actually train your dog to pee on anything that resembles a pee pad- for instance white t-shirts on the floor of your bed room, your pillows, your sheets, your bed etc.
Here you can see an example of what do with a little dog with extreme toilet issues. You can create a crate that only has a bed and a toilet. You can also create a exercise pen that consists of one small bed and the rest of the pen- pee pads. Then all you have to do is reduce the pads to just being in one of the corners of the crate.
P.s. Crates are a training tool. The goal is to train your dog to be calm and loose in your house. The more choices a dog has during the day, the less hyperactive and frantic the dog will be when you return home. Crates are useful when you don't yet trust the dog to not destroy your house, or your dog is not house trained. It is essential to teach your dog to love crates regardless of if they need one at home so that they are comfortable when they have to stay at the vet or in an emergency situation- like Hurricane Katrina.
My dogs are both loose in the house now that they are trusted.
Here's a tip for those with reactive dogs- when counter conditioning a new emotional response to dogs and people, sometimes its better to walk the dog in a new location to train. This could mean driving the dog there, but it is well worth the effort. This way you can start fresh and don't have to work against the areas on your walk that your dog has become sensitized to (like the dog behind the gate on the corner that ALWAYS sends your dog over the top). 
