So uhh..

I bought an 80×58cm bin online and when it came it was 80×58 cm, it's just that it tilts a little as it goes down to the base and I measured, the base was only 68×40cm. What should I do ((

Hi. I think you were originally wanting tips for a diy cage, is that right?

80 x 50 is a bit small for a hamster these days any. Guidelines are 100cm x 50cm (and for a bin that will be maximum measurements and it will slope down at the bottom and be less at the bottom). Can you send the bin back or not? What species of hamster is it for? If it's a Syrian hamster then the current bin won't work for the hamster, who will get very stressed. If it's for a Roborovski hamster, it might be ok for 2 or 3 months but they also need a lot of space - they are high energy.

It can be very difficult finding bins big enough for cages in some countries. In the US people usually get 200 quart bins.

If you're thinking of making a diy cage then Ikea hacks are popular and inexpensive (I'll link a thread about that). Do you have an Ikea? Which country are you in?

I am planning to get a new bin but I don't think there are any bins that are big enough available to me so maybe I'd consider DIY

If you don't mind some diy, what you could do is join two bins together. The way people do that is cut one end off each bin, slot them together and then maybe hot glue it (I'm not entirely sure on that last bit but I'm sure there'll be youtube videos about it

You then need to do something similar with the two lids to make one big lid that is meshed.

Connecting them together via a tube doesn't work though - it needs uninterrupted floorspace.

I live in Indonesia, ppl here r js finding out about proper care and the largest bins we have here are 90.5 x 64.5 x 47.5 cm, it's called the "Box Kontainer Shinpo 125l) what do u think?

It sounds good! Size is good. I'm curious - do you have a photo?