This research work is a expenditure plan of building maintenance for III. Gymnasium Osijek (High school of natural science and mathematics) for a period of 40 years, from 2015 to 2054. This research work refers to existing building of high school. There are no data regarding to construction costs, and the main reason for that was reconstruction of the building from 2006 to 2009 when the building was fully reconstructed and when energy efficiency certificate was made. The building is cultural heritage and it's over 125 years old. It's protected by Ministry of culture as cultural asset and it can't be removed or reconstructed before permission of advisory body. Data of all actual costs regarding to maintenance and usage of the building for the period from 2010 to 2014 was gathered for the purpose of this research. Maintenance costs and operational costs of the building are integral part of all expenditures and for the purpose of this research this data was collected in June 2015 directly from the director and staff of the school. Research of this data will help in the future development of a reasonable plan for maintenance of the building, allowing more efficient planning of costs and other-benefit analysis regarding to investment on the building as well. The total cost of maintenance and usage of the building for the past 5 years were 7.586.248,26 kuna. Following a detailed analysis of expenditures on maintenance costs and usage of the building helped creating a plan of building maintenance which can predict all costs in the next 40 years. Expenditure plan of building maintenance for the period from 2015. to 2054. contains following maintenance activities: 1. The costs of preventive planned maintenance 1.1. Costs of statutory periodic inspections 1.2. The cost-of planned works and repairs 1.3. The cost which will include replacement of used materials and elements 2. The cost of reactive maintenance 3. Operation costs