Hi guys,
Thanks a lot for your help.
The main reason to go with Aluminium than steel, is that the spot where I have to install the dish, is very tricky.
The balcony points to the north instead of south, so I have to mount a metal bar on my balcony so the dish can pass the house and point to the south.
So I have to mount the whole dish with the bar in a way it is very stable and still has free view to the sky. Plus the landlord doesn't allow any nails, screws or mounts on the roof.
A light weight dish is a huge benefit for me.