I am not a skilled DIY. I find that if you search eBay or your local DIY they sell good quality wooden boxes that you can customise.
For those that love woodworking and you're trying hard to discover detailed plans to build your dream project, you should check this link. They share list of 16000 projects with step by step plans. Each of the 16,000 projects are detailed enough to leave nothing to guesswork yet simple enough for beginners. Each projects included step-by-step instructions, cutting and materials lists, detailed schematics, views from all angles,.. It's easy to follow even I'm a beginner in this are.
The picture is just an example of the box I bought on eBay, its plain, sanded timber with a hinged lid. I bought 2 to go in my utility room as a storage. (40cmx30cmx23cm) I have painted them to match my decor. If you want a toy box maybe you can get your children/grandchildren to paint them or design the decorations. I can’t remember what I paid but it was less than £30