1. In what environment/network you application need to worked on – Internet/Intranet?
2. No. of you concurrent users your application has to support given some defined time frame, generally you consider 3-5 years.
3. What is the required through-put from the application?
4. Kind of servers that are provided to host your application(s), and what all technology set they can support.
5. What technologies you can use, and for how much time you would get the support from technology provider.
6. Is there any exclusive functionality requirement for you application, and what tools/tech are available in market to support the given functionality. This generally comes handy when you have to buy some tools for implementing functionality.
7. How much data storage capacity is required, and for how much duration you have to maintain the data. It may further require some archiving strategy etc.
8. No. of server(s) that would be available to host the application/database.
9. If there is any requirement for auditing/versioning of data.
There are some other Considerations
Maintainability: Most of the TCO of an app will be in maintenance, so you’ll want to make sure it’s easy to understand and work with. This also includes about to extend it — new functionality, features, etc.
Time To Market: Especially true for startups, as a slow time to market could potentially kill the entire business.
Scalability: When you build it using your sample data, it may be fast, but how well does it support the gigs of data it may have in a few years, or the thousands of new users.
Performance: Does it response in an appropriate amount of time. Everything might run great when you develop everything on your local box, but what about when it’s in production? Can your users still have acceptable response times even when they’re half way across the globe?
For more theatrical explanations
Ramesh's Blog 