Have an idea - general outline - what's the next step?

A good friend (and former colleague of mine) has put together a general executive summary of a SaaS product idea. She has an excellent presentation, good statement of the need the product meets, high level overview of functionality and the other elements of a marketing plan and quasi-business plan (minus the financials right now). There has been some real interest from potential customers as well as a VC.

She's a marketer. Seems the missing piece is how the product will be built and work (putting that on paper).

What should she do next? She's been trying to find a developer to partner up with her and help turn her vision into the general outline of a product on paper (detail how it would work) but they are close to impossible to find these days. Should she try and map out the specifications herself? Create a detailed MRD? ??

She's turned to me. I'm buried in my day job so can't give much attention to her efforts but I do want to help.

How should she take the next steps forward?

Thanks to all.

I think the next step should be talking to potential customers rather than building the application.
Based on their feedback she will be able to make a list of features, etc. Maybe even get some letters of intent. Ideally - upfront investments.

Once she does that - it will be so much easier to figure out what to do next, but I would definitely talk to as many potential customers as possible before diving into that.

Ok, some of comments say to try to sell first - but how can you sell something that doesn't exist?

My friend and I are developers and currently working on to find idea for our next project and one of our problems is how to be sure that our new products is going to be interesting to people so they will pay for it?

if is a web app she should start drawing her vison on any mockup program and then pass it to css/html directly. because html/css is very easy to learn and in any case she will start building up her product without wasting time.

The thing is she knows what she wants to build, does she know what functionality she wants it to have though? Having an idea is fine and all but from what I've learned, having an idea is only 5% of the total work, the development part is easy with the advent of Wordpress and sites like Themeforest. You need to get to know your target market to ensure your end product is tailored towards the needs of your target market.

Talk to as many people as you can is my advice. Don't email, but actually go talk to the businesses and people you want to target, ask them what they're using now (if they are) and then ask them what it is about their current product they hate and what it is they love and then, find a developer (even a cheap outsourced freelancer).

Development is absolutely the last thing you want to do. It can get you into a trap of spinning your own wheels and thinking you're making progress on the business when you really aren't. The most important thing is finding a market and paying customers who desire the product.

She might want to look into getting letters of intent and a volume of customer validation: getting customer responses, finding out what customers want, preliminary signups, commitments, preorders, etcetera.