When creating my Kroot Mercenaries squad for Golden Demon 2005 I faced the problem of doing a display base for models on round bases. Having no fancy drilling tools I looked around for usable bits and discovered that the lids of the flip top Citadel paint pots are perfect for the job. All it takes is a little clipping...
1. Save your dried paint pots...
2. Well, what really needs to be saved is the lids - or to be precise the lower part of the lids... (remember to clean the lids from dried paint).
3. Now, get out the clipper and cut away the outer rim of the lid.
4. With the outer rim removed the what's left of the lid should look like this...
5. ...and proved fine for fitting in round 25 mm bases.
To actually build up the displaybase I plan out the terrain with a few different height levels to make sure that the models that are to go on the base fit into a suitable composition that presents the miniatures in the best possible way. For filling the areas inbetween the cut-up lids I use lots of different materials - gravel, glue, cardboard, different fillers for house-decoration, and of course thematic bits from my bits box.
Now, before you ask about the Krootox (e.g. a fitting for 40 mm round bases) I must admit that I had to construct that one with a strip of plastic card - works fine, but it took a little more work...