Hi, Dale, el jefe's account above is an excellent guide. I recently chose this method myself on my first build, an FLO #8.
Just to add a few of thoughts; the reason I used this technique was because I read a forum post by a UK rod maker re: guide charts: They're fine if you have that maker's blank model but otherwise .... well, all blank models flex differently from one another.
Having splined the rod, lightly glued the tip ring in place & marked the spline on the sections, I roughly taped on the rings. I then set the rod up at about a 60 degree angle, ran a line through it and clipped on a light weight just to add a touch of tension to the fly line alone.
I then used a large paper clip hung on the tip ring to suspend a plastic bag with another light weight in it. This places the strain on the blank not the taped rod rings and makes moving them later easier than if the load was directly on the fly line. (I do like the rubber band idea, btw.)
The light weight in the bag should only flex the tip section, so adjust those eyes as el jefe says above then add a bit more weight to the bag to flex the next section. Adjust the eyes there, add more weight and do the third section from the tip. Common sense should suggest where the stripper ring should go - often on that third section leaving the butt section ringless on a 4-piece, but that could depend on the handle you choose. If in doubt search on line for similar models and see where they've placed it as a guide.
By the end it should just ''look right'' to the eye, as smooth a curve as possible throughout.
I wouldn't worry about an ideal ring placement landing on a ferrule until it happens. At least with this method the whole thing is flexible until you're happy with it rather than feeling you've compromised some set rules.
One of the most liberating things I found about making my own rod was realising that nothing was set in stone. I whipped and epoxied the whole thing then decided I'd over-whipped the eyes and didn't like the thread colour either (I'd used a colour preserver on Garnet and Gold and it all looked rather '60s
). Three days later I stripped it back to a blank & handle and re-whipped it how I now knew I wanted it. I'm now really pleased with it cosmetically. As for in practice, well I tested it yesterday with a Barrio #8 WF and it's a rocket-launcher! I'm no great distance-caster but I exceeded my own expectations so I guess the above method does work and I'd happily employ it again.
Good luck with yours!
Lewis.