I'm looking to buy/build a road bike and I would like it to:

• last 100 years
• have a low environmental cost

As I'm not interested in shedding grams (a diet would be more helpful for me), I'm leaning towards a steel frame. But steel frames are often cheaply manufactured, and the price is slowly starting to reflect trendiness than quality.

How do I recognise a high quality new or used steel frame? Are there simple things to look for when weeding out the poorly made or overpriced frames?