A lot of IT consulting may involve writing or configuring software and systems. And before that, requirements analysis. So it's not something that you can estimate realistically.
And neither the consultants nor the hiring company can afford to really get the raw end of a deal.
If you think you have information or skills with Windows VMs or whatever that is very valuable then you can certainly try offering some fixed fee for some particular outcome.
It is likely the real requirements will not be available until a qualified person spends a significant amount of time doing that analysis. So the desired outcome will change after the contract is signed. So will the estimated amount of effort and you may also find that you don't even necessarily have the staff to handle the requirement.
I think the amount of effort to successfully deploy projects, unless they are extremely routine, often does not leave as much room for profit as you might think. Especially if increased hours do not add to the fee charged. It becomes a conflict of interest where one side wants to squeeze as much work out as possible and the other wants to do as little as possible. So having a useful outcome can be a casualty of that.
