It is not clear whether you are referring to Site Cabins or rental of an Office, but under NEC this would be categorised as Equipment, as it is used to Provide the Works but not included as part of the works.
Under the Schedule of Cost Components the cost could possibly be allocated to one or more sub-categories of Equipment, depending on how it is procured.
The WAO charge is calculated by applying the percentage for Working Areas overhead stated in the Contract Data to the total of People items 11, 12, 13 and 14., so you would only apply the direct Fee to the cost of this accommodation.
Note that the accommodation must be within the working areas to be classed as defined Cost, so if it is an office near to the Site but not within the Working Areas, it would be necessary to add this to the Working Areas, not least to capture the cost of People working in this accommodation who are Providing the Works.
Under the Schedule of Cost Components the cost could possibly be allocated to one or more sub-categories of Equipment, depending on how it is procured.
The WAO charge is calculated by applying the percentage for Working Areas overhead stated in the Contract Data to the total of People items 11, 12, 13 and 14., so you would only apply the direct Fee to the cost of this accommodation.
Note that the accommodation must be within the working areas to be classed as defined Cost, so if it is an office near to the Site but not within the Working Areas, it would be necessary to add this to the Working Areas, not least to capture the cost of People working in this accommodation who are Providing the Works.