The sort of "standard" for ex-pens is 8 24" sections (the height varies from 24" up). These are the typical wire ex-pens like Midwest. These are perfectly adequate for Havanese. Most of mine are 24", though I have one 30" one also. I prefer the 24" ones because they are easy to step over, to get in and out to tidy up. In my experience, and talking to many Havanese owners, very few Havanese actually JUMP out... If they are intent on escape, they climb. And if they can climb 24", they can climb 36 or 48". The problem being, that the taller the ex-pen, the greater the fall on the other side and the more danger of injury. So as far as I'm concerned, if a 24" pen doesn't keep your dog confined, you really need to consider crating rather than an ex-pen. All of mine respect the ex-pen, and although Kodi can easily stand with his front feet on the top of the 24" pen, and his head and shoulders much higher, even he wouldn't dream of challenging the space. It's a comfortable "den" area, and they all stay put. These wire pens can be either expanded indefinitely by adding on more ex-pens (we use three for a "dog yard" against our travel trailer when we are away from home) or can be folded smaller during potty training... down to a 24" square. When Kodi was young, we attached a large crate to the end of a Midwest pen for his "apartment". He was in this pen arrangement when we were away from home and at night. We put it away when we remodeled our house, and he started sleeping in the bed room (in a crate) and when I went out during the day, he was gated in my office. That's what we do with all of them now that they are all reliably potty trained. The Midwest pens fold up easily, are not very heavy, and are easy to throw in the back of a car. They are NOT airplane-friendly, but I don't think any useful ex-pens are. One other good thing about this type of pen (Iris pens too) is that you can ALSO use them as gates to keep dogs out of things on a temporary basis. I've set them up around areas I am painting to keep the dogs from touching wet paint, have used them as an extra "safety" barrier around back yard gates when we have guest dogs, put them around our blueberry bushes to prevent unauthorized pilfering
We also have a metal tubular frame ex-pen from Best Pet. This is a MUCH heavier pen, and each section is 31" long, so the smallest area is larger, and it's quite a bit bigger when all sections are used. We have this set up in the corner of our dining room in a 1x2 configuration, which is plenty big for a UgoDog in one end, a bed in the other end and some place space between. This has been our "puppy storage spot" for both of the girls while they were growing up. We still have it up so that we can separate everyone at meal time. Kodi gets gated in the kitchen, Pixel eats loose in the dining room and panda eats in the pen. These pens are VERY heavy, and are best left in one place. At least _I_ wouldn't want to move it around with any regularity!!!
Iris (plastic) pens are also 24" sections, and I believe you can add as many sections as you want. They are bulkier than Midwest wire pens, though they are no heavier. (maybe a bit lighter) It depends on the dog whether these are a good choice or not... If you have a chewer, probably not.
A lot of breeders use Iris pens for litters because the plastic surface makes them easy to keep clean.
Richell and another brand that someone here uses and likes, (can't remember who!) makes prettier "furniture" style pens. Those are a lot more expensive, and although I believe you can make them longer or shorter, the width measurement cannot be changed. Even those are adequate, space wise, for small-medium sized Havs... and even for bigger ones, these pens definitely are roomier than the average crate. Only you can decide whether the decor aspect is worth the tradeoff in terms of price and space for the dog. Not sure of the portability of these since I've never worked with one.
I would NOT recommend the cloth pop-up style "play pens" for dogs older than small puppies, nor would I ever leave even a puppy in one unsupervised. These are fine for short-term confinement if you are sitting right there with the pup, but are too easy for a pup to destroy, roll or climb out of. Plus they are really not much bigger than a crate. The plus side of these is that they ARE very light and portable.
Below are photo of:
1. Kodi's Midwest pen/crate "bed room" when he was a puppy
2. The BestPet tubular steel pen that Pixel and Panda have both used
3. Our "dog yard" against our travel trailer. This is 3 pens attached together. It is easy to set up and take down, and light weight enough not to be burdensome. We set it up if we are going do more than just stop over night on the road.