To estimate the costing for a steel structure building cost in Sri Lanka, you’ll need to follow these steps:

1. Define the Scope: Determine the size and purpose of the building. The cost will vary depending on whether it’s a residential, commercial, industrial, or institutional structure.

2. Architectural Plans and Design: Have detailed architectural plans and structural designs prepared for the building. The design will impact the amount of steel required and, subsequently, the cost.

3. Material Quantities: Work with a structural engineer to calculate the exact quantities of steel required based on the structural design and building dimensions.

4. Steel Prices: Research current steel prices in Sri Lanka. Contact local steel suppliers or refer to construction materials pricing guides to get the latest prices.

5. Labor Costs: Contact local construction companies or contractors to get quotes on labor costs for erecting the steel structure. Labor costs can vary based on the complexity of the design and the experience of the workers.

6. Foundation and Site Work: Consider the costs associated with site preparation, foundation construction, and any additional materials needed.

7. Miscellaneous Costs: Don’t forget to include other expenses such as permits, transportation, and overhead costs.

8. Contingency: Add a contingency factor to account for unexpected expenses or price fluctuations.

9. Calculate the Total Cost: Once you have gathered all the necessary data, calculate the total cost of the steel structure building by summing up the material costs, labor costs, foundation costs, miscellaneous costs, and contingency.

Keep in mind that construction costs can fluctuate over time, so it’s essential to regularly update your estimates if there are significant delays between planning and execution. Also, consider consulting with local construction experts to ensure accuracy and efficiency in your costing process.