I did two bases for my Chaos Spawn project, and both were scratch built, and thought it would be fun to share the process.
Start with an idea of what you want to do before anything is glued down! Here, my thinking was a destroyed science facility. Interestingly, it was only after completing these that I realised I'd used a similar theme with similar monsters last year (https://nerodine.blogspot.com/2019/07/roman-lappat-beginner-course.html) and pretty confident I was subconsciously influenced by this.
Blue cylinders are pieces of plastic straw, with some old cables from discarded PC parts glued inside. After that, it's a combination of leftover items from my bits box. So there's pop-out pieces from MDF terrain kits, some cork tiles I ripped up, Necromunda belt kits, basing paste, little cut offs of balsa wood. Anything to add to the feeling of a building that's been utterly destroyed.
When the larger items were firmly in position, I generously applied superglue over the empty areas, and sprinkled large gravel in, and then very fine gravel to fill the inbetween spaces.
The last step was ensuring it was all properly dried, then applying a dilution of PVA and water over everything to lock it in position. Leave for a few hours, then it's rock hard and you won't risk the gravel falling off.
There are large, flat surfaces here, despite the appearance. That's deliberate to ensure the monster feet have somewhere to
securely place.I went back and forth checking it was still a good fit.
Black primer, then a harsh zenithal. I was pleased how coherent it looks at this point. There's something very pleasing to a well primed item.
Riffing on the colours used on my Chaos Spawn, I've tried not to focus on picking out elements of the base - rather just the feeling of a lot of rubble.
Highlights, such as they are, are just from the bluer end of the colours used on the Chaos Spawn. A little red and pink is added to the lettering to give an area of interest, but you won't see most of it when the monster's glued on top - so there isn't any point spending too long here.