I am playing a gig and want to have a song that each band member (guitars, bass and maybe drums) can take it in turn to have a solo. It needs to be a song or part of a song that sounds good if it just keeps playing round and round. I was thinking something like the outro to Walk This Way by Aerosmith or the opening riff from How Many More Times by Led Zeppelin.

Can I get some suggestions from you fellow musicians? Preferably not just 12 bar blues.

I'm doing a covers set and there are probably a lot of good songs out there to solo over. I just wanted to get some ideas
I play the guitar. I usually improvise over these
(led zeppelin)
black dog
stairway to heaven

Sunshine of your love

bon jovi
you give love a bad name
bad medicine

knocking on heavens door

my advice to you is just play any song you roughly know. Then improvise the parts you don't. Simple.
Well, it could be any song that you and the other musicians know fairly well. During a break in the song or towards the end, everyone can take a turn at improvising over it.

Other than that, you can do Knocking on Heaven's Door. It's a simple 3 chord song that many people have covered live. Guns N' Roses have done long and extended versions of the song with long jam sessions. One of my favorite versions of it was when they played in Tokyo back in '92/'93.
Skip the username, call me Billy