It depends on the exhibitions.
So exhibition organizers only you let you use their stands/stalls with limited options for changes (less common), some refer you to a list of 'approved' stand installers/designers (fairly common), and others let you do whatever you want so long as you follow a few basic safety guidelines (and stay within your stand limits). For the last option, there is a wide variety of service providers.
I am in touch with an international stand creator - they create very unique stands, but they aren't cheap. If you have a high enough budget and are in the US or Europe, I could connect you.
Are you planning to generate leads or sell your product at the exhibition? If you are doing either of those things let me know and I'll be glad to give you some pointers for generating a lot of leads or sales at your stand. I do this for a lot of businesses who want to maximize their time at exhibitions and shows.