Oh my. I did as I said in the previous post and tried the hacksaw for cutting this steel. I recommend you don’t do that. I went to buy a suitable tool instead. I think this picture explains why.

Anyone who have done this before is probably laughing. And those who have not can hopefully learn from my endeavors and mistakes.
My further recommendation would be to cut the sides of the rail with two straight cuts about 2 mm apart, remove the shred and then fold as in the upper two pictures. The reason I wanted to do as in the lower two pictures and cut away the double sheet layers was that I want the wall as close to 7 cm wide as possible but the extra mm (1/32″) you get by folding the edges on top of each other is perfectly ok and definitly worth the time saved.

Now I measured and made the bottom rail the correct length. I removed part of the foam to ensure I got the right length since the end piece of MDF will be mounted against the steel and not the foam. Note that the MDF sides will not go all the way down. I will leave room for the parquet flooring to expand underneith.
Then I used the leveling laser to find out where the cieling rail will be and cut that the same way.

Haha! I censored the electrics. You should always respect electricity and don’t leave bare wires. In this case I made sure that it’s safe and double checked and triple checked. It’s not worth it to take any chances at all.

One more thing. I have clicked many shortened links in my past not knowing where I would end up. I’ve clicked them on twitter. I’ve clicked them in chats, fb, reddit etc. But I have not clicked them on a piece of construction material. Not until today.