Recommend you look here:
http://www.280group.com/productroadmaptemplates.htm I like a lot of the information and tools that this group has.
And I would say strongly that a product roadmap is good and important. You need to have a general idea where you are heading with the product, the time to get to various phases of that and the resources required. It also is the foundation for other functional activities. For example marketing. There might be a significant product upgrade that I build a marketing launch plan around or a specific feature that let's me pursue a new market segment. The roadmap is a coordinating point for all that. A successful company is, at the core, about having a product/service that offers value to users and is uniquely differentiated from the competition. And stays ahead of the competition...and continues to deliver more value that users need. The roadmap gives you perspective on where you are against those objectives today and where you'll be in the future.
Uggh. A road map? This rarely seems like a good idea. Unless you are maybe building say a giant corporation like a bank, and all sorts of people need to review your 2 year roadmap for compliance to laws and regulations.
You have an idea. Hopefully, your idea is going to help you accomplish something you need yourself. Just start building whatever it is that's going to help you start accomplishing it. Don't waste time documenting some dreaming of what all these features are going to be. Laser in on one feature. One page. That does the thing that your stuff is going to do 90% of the time. And just start molding it. Give yourself a goal of having it done in 2 weeks and then you are going to invite others to it no matter what condition its in.
It's how we build everything at Inkling and it works much better than anywhere else I've worked. Even at Inkling, we'll catch ourselves having a long phone conversation about where some features can go. Danger. Tomorrow you'll probably have a new idea, or some more insight from your customers that you need to reflect on and start molding your app differently.