Is it permissible to use a percentage in charitable projects, such as 5% for building mosques?

It is permissible for those managing charitable projects to take from donations in exchange for their work, as the sustainability of these projects usually depends on that. The amount taken should be determined by custom and necessity, without excess or extravagance. The donor must be informed that a portion of the donation will be deducted for operating expenses, such as by displaying a sign clarifying the expenditure percentages.