It is very important that when you are making your decision of where to buy your steel walk doors that it is based upon both the quality and price of the door that you will be purchasing and entirily upon the convenience of proximitiy.
You must make sure that for every building, you consider the application and usage of each door. There is a guide that can help you with this, it's called “the Selection and Usage Guide” and was created by The Steel Door Institute. This guide can help with exterior and interior applications and is an excellent guide to help you determine your choices. Basically the tougher the environment and the more frequent the usage, the more probable the need will be for heavier gauges and higher grades of hardware being used. The mainity of doors being used are a standard 20-gauge door however, a heavier 18-gauge door is probably the most recommended choice for entrance doors especially with higher traffic requirements. You may also be looking at a heavy duty Grade 2 lock or a Grade 1 lock which may be necessary in this situation rather than light or medium duty Grade 2 or 3 lock. There is a huge variety so it's important to research your options thoroughly before making a final decision. There are several other things that also need to be considered such as grades of door frames, grades of locks etc.
Another typical choice is the door core. Exterior doors should have an insulated core, with polystyrene or polyurethane filler. Polystyrene is the most common and cost effective and typically carries an R-value of around 4-5 and make a great choice for steel buildings . Here is a little bit more info on Polyurethane, in case you are not familiar with it. They are widely used in high resilancy flexible foam seating, rigid foam insulation panels, microcellular foam seals and gaskets and much more. It is any polymer consisting of a chain of organic units joined by urethane (carbamate) links. Now back to the R-Value, something to consider on your door is the R-Value. This will include the frame and components of the door. Because doors are constantly being opened and closed, the seal on the door has a much greater impact than a static door R-Value and this is based on the warm and cold air that passes through the system. So you need to ensure that the doors are well sealed through a high quality screw on or kerf type weather seal and the cost will illuminate your need for a polyurethane core including the best economic fit is provided with your new walk door. All in all following the instructions and recommendations set forth will help ensure that you can both easily and accurately make the best choice when buying your steel walk door (s).