I believe the Contractor should own the float, however the float should be communicated with the owner. For example during contract negotiations two dates should be agreed upon, Date of Completion and Date for Pratical Completion for the project, the total number of days between these two dates is the Contractors float. If the Contractor has any delays the number of days will be reduced, however if the Prinicipal delays the project a new Date for Pratical Completion should be set, this includes any delays due to wet weather.