Birthday cake for 20

[pico1]

My DS is having a joint birthday party with 4 of his friends and I have volunteered to make the cake. There will be at least 20 kids there. Am a competent baker but am struggling to think of anything other than a giant tray-bake type thing. Has anyone any ideas for a “proper” cake that would feed 20-ish kids. Thanks!

Most big cakes will feed 20!! They don't need a huge slices
You can also get more bits out of a cake if you don't cut wedges and cut into squares

It all depends how you cut, rather than how big your cake is necessarily.
I made a slightly larger than usual cake last year for my daughter's birthday party, and used a guide like this to cut into enough pieces to serve 28.

Thanks all. The cake-cutting guide is super!

I did a small cake then individual cupcakes for party bags (already wrapped up)

For big parties (whole class) I have done One of those big traybake things but taken out of the tin and decorated like a normal cake. Always loads left over.