Thanks for the various inputs and comments, all very helpful stuff.
In the end I decided to go down the iPad route as it seemed the simplest way to get a quick result, a key factor given how crazy busy life and work are right now. Anyway I have captured some some lapse footage using lapse it (the paid for version). There have however been a couple of issues. The minor issue is that lapse it has projects, and each time you shoot a lapse you can either start a new project or append the footage onto an existing lapse. I chose the latter option to keep everything in one place. However this means you end up with a LOT of frames and the iPad struggles to process it and keeps failing, also lapse it has basic editing facilities to trim/cut unwanted frames. This works well on a single lapse, but where two lapses are appended I keep getting little loops of frames which obviously doesn't work with a time lapse of building something, you build a bit and then immediately build it again. Anyway these issues are relatively minor, frustrating I this case but in the future easily worked around.
A more fundamental problem is having a three year old who knows how to access the iPad...
I have some footage which I will attempt to get onto Vimeo and stick on here if people are interested once I've finished the build.
