Not everything will be by sf or 20%. For instance, landscape, improvements, fence, parking lot, curbs, grading for runoff, might be half done to accommodate that unit being ready for business. You'll need to take it by asset type. Engineering and architecture will typically be a %. Furniture and fixtures are going to be specific to the unit. What you are looking for is indirect (common) and direct CIP. I find it helps to have separated this while in progress, where possible. Final build-out always seems to end up customized.