Tibnor and similar can answer about sizes, but they know nothing about what you need. For that, unfortunately, you need a structural engineer. You might think that as a salesperson, you should know a bit more than that it's a piece of steel.
The technist's bible, Karlebo Handbook provides the answer to your beam questions. Or maybe you can manage with this: http://www.tibnor.se/C1256EF1005D76CD/0/FF4D7759832DECB3C125701C0045813C/$file/Handelsst%E2%96%A0lkatalog_2005.pdf 
Check from page 8.
Check from page 8.
I saw a small truck that had Huddinge Stål written on it. I called them and got guidance on which dimension was suitable, with quite a bit of belt and braces. Much cheaper than hiring a designer, etc. Bought over the phone, and the beam arrived home rust-protected and nice two days later for a small shipping fee. About the same price as laminated wood but more compact...
Borrowing the thread a bitsigpl said:
I am also looking for an I-beam that should be about 20m in total and should be for a hoist.
So the beam must support a weight of about 500-600 kg on the hoist with a carriage.
I expect the beam to be attached approximately every 60-100 cm.
The beam should ideally be between 80-100 mm wide and as low as possible, to maximize lifting height.
Any idea what height I need to accomplish this??
I want it to be as cheap as possible.... ;D
The normal problem with beams is that they experience significant deflection because they need to span a large distance. In your case, if you're going to attach at 600/1000 mm, that's hardly the issue; rather, it's the attachment points themselves. I think you can check Tibnor's catalog and find a suitable beam, attach it properly, and forget that it wouldn't be able to handle a 1000 kg load.