Hey Bob, I built mine out of acrylic that I bought at the hardware box store. The best one I did was for the Vallejo paints, and it gets used a LOT.
Things to consider:
Being able to see/ read the color of and/or on the bottles
Basic strength. A lot of bottles on it will make it heavy. My Vallejo rack is actually strong enough and stable enough that I move it around a bit.
Flexibility for different paints. Pick a paint bottle size/brand to fit in the rack, then see what other brands are close to that size. You can't make the holding parts too oversize as the bottles will slide around and fall out. Too small and the bottles will not fit. Make it to fit reasonably some fixed brands bottles.
Here is a paint rack I made that fits MRP and Alclad II paints along with another brand that is now discontinued and the paints are turning to gloop.
It works great for the Alclad paints and MRP. All the Vallejo have their own rack now.
Here is the paint rack for just Vallejo paints. I have a number of the larger thinner and primer bottles and those are no problem to deal with.
This works well at least for me.
Just some ideas to help with your design and use issues.
Note the MRP paints also fit the Vallejo rack just fine.
