Add custom option "Sizes" to all products in Magento store

Simple. Magento store with less than 100 products (~80). All products need custom option called "Sizes" entered. >> NO SHORTCUTS THAT BREAK PROPER MAGENTO FUNCTION << (if admin click 'edit product', tab 'Custom Options' should show "Sizes" and be editable) Once awarded entry must begin immediately and take no longer than 1 business day to complete. If developer does quality work there will be a follow-up project awarded as well. Low bid very important for award. Good Luck :)