There are no inputs required for postable command. You can just call RevitCommandId.LookupPostableCommandId’s.
I would like to do that with floors
Why? You can create floors without the need for postable commands. Postable commands are a last resort only, and should never be used in automation unless you literally have no other choice… And even then they are ugly (sort of like substituting a screwdriver for a sledge hammer). Dynamo coupled with the Revit API is comprehensive enough that you won’t need postable commands for like 99% of cases.
If you have a particular case that you can’t do (and you have a script where you have tried), then I would recommend creating a new post with what you are trying to achieve and the script that you are having issues with.