Certifying a single Building within a Complex - energy metering

I have a query with respect to our Building and an aceptable level of energy metering. The building under certification is one of several buildings however has common heating and cooling production. Knowing that metering needs to be installed to obtain an accurate level of energy usage, the first thing we did in order to be able to certify was to install electrical metering to capture this energy usage in our building. This covers us for the chillers as they are electrically-run, however the heating is produced by boilers which are run by gas-oil and distributes for the whole complex. Additionally, the utility bills we receive are for the whole complex however we can gain an accurate proportion of these by dividing our energy use % into that used over whole complex. In order to gain an accurate heating ratio, given that this cannot be separately between buildings (without significant cost and technical difficulties) we wondered whether it would be acceptable to obtain this usage by measuring thermal differences in water supply and return in heating production together with flow rates of heat pumps and measuring our building thermal consumption with thermal submeters, and in this way calculate the proportion of gasoil consumed by our building compared with the entire complex. Hope this makes sense and that someone can help me out. Thanks.