Here is quick view on Mybuild 1001, base kit frame pack. Really decent one with hell lot of articulation and compatible with bricks like Lego. You can make great deal of robots with this, going to buy more soon. I got it for a very good price from Amazon . Enjoy building.
It comes with a lot of customization options, you can take the existing bricks in your hand and then try to attach to this. I have done a base customization as you see in the featured image. Added some robot arms and all. Great job my build https://www.mybuildtoy.com/mechaframe
https://amzn.eu/d/4HtnfPD