The concept of "build it and they will come" may be a good approach for pyramids and baseball fields, but not for engineering projects.  Good engineers are creative and come up with plenty of ideas about features for products and tools for better engineering practices.  But what they do with these ideas can make a big difference in your team.  Many engineers believe if they have an idea, they need to first build it into a solid feature or tool before sharing it with others.  If you build it, how do you know "they" will come?  How do you know your idea will be received well?  How do you know that people will want to adopt it?  The only way you will know this is by sharing your idea *before* you turn it into reality.  You need to describe what problem you are trying to solve, what user scenario you are completing, what gap you are trying to fill, or what savings will be generated (cost, time, etc.) with your idea.  If you are leading teams, you should help your engineers feel comfortable with sharing their ideas.  Communicating ideas has many benefits.

1. You will see how high the interest is from customers or other users and therefore know you will have people adopting what you are creating.
2. You will find out if someone else is already steps ahead of you in creating something similar.  Reinventing something that already exists is costly for an engineering team.  Of course, if you find out something similar already exists, that person probably didn't communicate their idea out broadly enough which is why you didn't know about it.  Shame on them!
3. You will find that others may have similar yet slightly different ideas which when combined may not only make your idea better, but you now have others to help you turn those ideas into reality.  Teamwork is awesome!
4. And the harsh reality of it all, if you work in a corporation, "your" idea on a feature, tool, process improvement, or whatever, is really an idea for the benefit of the company.  It's not yours to own, it's the companies.  So you need to be willing to freely expose and sometimes even give up your idea to others who may be better suited to implement it.  The benefit of communicating your idea is that it helps the company and since they give you a pay check, it's a good tradeoff.
5. An additional benefit of communicating your ideas broadly is that no matter what decisions are made on how to proceed with implementing your idea, you can get credit for the idea because you have communicated it so many people that nobody would question the owner of that idea.  If only a few people know about your idea, and then a coworker finds the time to make it a reality (and communicates that more broadly) that person will potentially get credit for it and you just missed an opportunity.

There are many ways to describe your idea before fully implementing it.  Try creating user scenarios, story-boards or UI mock-ups, diagrams or models, documentation like a gap analysis or one-page proposal document.  You can do a prototype or proof of concept although you should consider running your idea by some people before even getting this far along.  Then set up a meeting and get the key people in the room like those that need to be in agreement for you to move forward with implementation as well as those that may use what you are planning on creating.  Gather feedback from all of them and be willing to adapt your idea as you receive input.

At the point you are ready to build "it", you should know who will come to use it and in what way.  You need to do this upfront planning and communication because if you build it and they don't come, you have wasted your time.