I have many € 1 filaments bought from amazon and China, I started organizing them and so I created a modular spool.
The material is about 10g for Spool End, 13g for 5/10Meter spool and 15 for 20Meter.
You can complete a spool combining a spool and a spool end or 2 same type of spool.
You can use this spool as singular or create a battery of spool, in battery You can save some material using the back of existing spool as top.
I add a filament holder (even if I put hole in the spool).
But the photo explain better.
If you need some other dimension ask without problem.