Estimating Improvements and Maintenance Costs

[Christopher Madden]

It seems to me that one of the most subjective numbers when analyzing a deal is the improvement/maintenance costs. I have heard a fair number of horror stories regarding inaccurate budget projections. Obviously these are never going to be 100% accurate, but what are some measures you can take that will help mitigate risk in this area specifically? Is it just experience based knowledge, are you safer overestimating, etc?