how to divide shares for unknown valuation
brk: You need to make an honest assessment of what value prop you each bring to the equation.He has an idea.  You can implement it.  How many other people in his reasonable circle of contacts (meaning that he might actually have to go and look for someone) could implement his idea on-par with you?It does not matter that you are "the technical guy".  If (for example) his idea is to create a forum targeted towards people who have imported right-hand drive cars to the US, well, that's little more than installing a few basic packages and there are 8 million people who could do that, which makes your unique contribution very marginalized.If his idea encompasses things that you have more specific domain knowledge of, and more value-add, then your unique value goes up significantly, as does your appropriate % of the equity.Most likely, it's somewhere in the middle.  He has an idea that to implement might be 80% "work" and 20% "invention".  You're probably the best guy he knows for the job.  I stress knows, because there are probably 10,000 other people that could do equally good work, but they are an unknown to him.  This gives you an edge, but it's on the order of a few %, not a few dozen %.  At some point it would be more valuable to him to find 1 of these other 10,000 people and take the risk instead of doubling your stake (again, generalizing somewhat, but you get the idea).Conversely, how easily can you find another "idea guy" who would also make you a good deal?  If you have many "idea guys" to choose from, then his unique value to you is diminished and he would have to lure you to his project.If you are just loping along in life and have no better options, you're probably looking at something in the neighborhood of the 1:9 he proposed.  If you have better/more valuable/more lucrative options in front of you, you're probably more like 1:5.  If you have a solid track record and have been-there-done-that (which I don't suspect, else you wouldn't be asking this question...) then you might be 1:1.