First I just needed something simple so I made my first iteration:
https://www.printables.com/model/568089-modular-spool-rack-with-pvc

Now I have more spools and I needed more storage, so here is iteration 2!
This iteration still uses 32mm PVC pipes with 3mm thickness from my local hardware store.
The holes in were these pipes go have a chamfer so they get squeezed in.

How this works:

This iteration consists of 2 different models with 2 variation.

Top and Bottom, Top is for your top most layer, bottom for any other layers.

with_bottom, these include holes at the bottom to stack layers on top of eachother.

_support: these are for when you want a longer rack but don't have long or strong enough pipes.

For a basic rack with 1 layer:

2x Top

For a basic rack with 2 layers:

2x Top_with_bottom
2x Bottom

For a basic rack with 3 layers:

2x Top_with_bottom
2x Bottom_with_bottom
2x Bottom

You can always use the models with_bottom if you are not sure if you want to expand later! They don't sit in the way of anything.