Lego Baseplates. Are the only cool ones from old sets? And general advice.

Today I stumbled across a post (post link)on Facebook where they were asking for help identifying a base plate a friend gave them.

It was a really cool base plate from an older Lego Alpha Team set.

That said, it's awesome. I am curious if there are other bases like that out there. Or maybe, can bases be customized and made? I don't know. Anything is probably out of my price range. But with two little boys, the imagination play that could come from a variety of plates like this, it would be worth it.

I have only ever seen the square basrs Lego makes in like 3 or 5 colors and two sizes.

Please feel free to inform me, overwhelm me with the knowledge of these types of pieces.

Have you seen different ones? Used them? Do Lego stores carry things like that?

While at it. Are there any sets or pieces that you recommend for that kind of play?

My youngest, his imagination is out of control and I want to foster that. At six he is very bright, but not a strong reader yet. I could see baseplates being a hit. Not sure what kinds of sets or pieces would be good to add in to what he has. He absolutely will build a nice $60 set with me and his dad or his big brother giving guidance... then will start to alter it within days.

My oldest is only ten but he is building sets that are 18+, and pretty much anything that looks cool or amazing. So I am always looking for build recommendations. Mechanical ones he loves too. Right now the Galloping Horse one is on the wish list and the Japanese Cherry Blossom Art. The Ninjago City Workshop looks like it might be a nice intricate but interesting set but I'm not sure.

He's even building a Mould King cyberpunk clock and recently completed a ROKR Marble Run builds and I'm have another hidden away to give him so that he can build it... and see what he has to alter to add that to his current one. I figured it would be more challenging than giving him the two at once and building them together the first time.