The Storm Dalek uses the same base and skirt footprint as a NSD Dalek. If you don’t already have the Dalek Builders Workshop manual (http://www.projectdalek.co.uk/) , I would strongly recommend you become a member, pay for the manual and get the free additional manuals for the 2005 Dalek and the MK6 manual.
As for the base I recommend 3/4″ grade 1 or 2 plywood. At this phase I also apply the varnish (which you can get at Home Depot or Lowes). This is very important and necessary step. It protects the wood from warp-age. In the first photo here the problem with the base is that the wheels are too far forward. This makes the Dalek too sensitive and difficult to steer remotely.
I have moved the wheel spaces and motor mounts aft. The undercarriage lights are added as well as other access points. This gives the illusion that it is hovering as it moves down the hallway and washes out the wheels so you cant see them.
Since my Daleks are remote control, it is very important that the base not only be very stable so no “wheelies” ever occur from a sudden, rapid acceleration, they also do not lean in turns either. No wheels should ever show while it runs down hallways or on reflective surfaces while the under carriage lights are on. I have seen some Dalek builders use the wheels to help stabilize the platform because their main drive wheelbase is too narrow, too far forward or both. As a result, you have a sub-optimal design and an unstable platform. That means it is unsafe.
For drive motors, I always recommend NPC 24v drive motors with the brakes removed. New motors are expensive. What I have done is visit Craig’s list and get a old wheelchair to strip down. I use those motors, wheels and sometimes those batteries and chargers if they are 24V and working. Look hard. You can get very good deals. I got all I needed for 125.00. Those new NPC motors are 325.00 + motors EACH and that doesn’t include the wheel, charger, batteries or other wheels you could use to help stabilize your Dalek.