I am not sure what you mean about different lengths.
The Ovo tubes are ALL usable with the Playground. I have the Playground and I attach it to many things using the Ovo tubes.
If you are wondering which tubes are the best to use for attaching things, I would say all of them are very useful EXCEPT the u-turn tubes. I have 2 and never have i used them. the ones I use most are these:
Ovo Elbow
Ovo Tee
Ovo Curve
I also recommend the Ovo Trainer Exercise wheel (but do not use the black rubber band it comes with - the smell is quite strong and hamsters will avoid it). My hamster loves this wheel.
The parts i mentioned above allow the most flexibility when trying to connect one cage to another. This website has the cheapest prices I have found for the UK but I am not sure if they ship to Poland. petplanet.co.uk
Since you want to use the tubes to join up above the playground you will definitely need curved tubes, not straight - the reason is that on the playground, you can see the tube entry holes are on different places on each side. With the curved tubes you can make them meet at the top.
Let me know if that answers your questions or if you had something else in mind. I have a TON of Ovo things and I also have the playground. so if you want me to check which pieces can connect 2 cages together, let me know which cages and I can take photos for you and list the pieces.
I will get my Playground out and take a few photos for you of the different types of tubes attached to it if you think it will help you. It is great that you are adding on because the playground is so small by itself.