I have begun creating my first train set and decided this is a good medium to document my progress, as it worked well for me on my trip. It may not have worked for others, but it matters less for this anyway.
I have been planning to start a set for a while and was given a starter set of track as a present. I've been throwing grand ideas around of large circuits, computer controlled systems, turntables, automated operation and so on. I decided that my chances of getting that all to work first time was slim, mostly as I had no idea how to do the physical construction and what the limitations where, so I scaled down.
My first set is a simple double loop. The rail is not isolated so only one train will run on it. There is a small siding. This allows me to concentrate on the details I didn't know how to do: mounting, hills, tunnels, bridges etc.
I had a basic plan from a book which I was scaling to suit. After spending hours with a calculator, square, metal ruler and pencil making marks all over the base board I put the track on and found out it how much more track I needed. I went out to get the track (turns out there are no hobby shops anywhere near Eltham, why is this?) and came back with a train, two carriages, a bridge and more than enough track. Assembling my newly completed layout proved that is just didn't fit it my carefully scaled and drawn notations, so I just fudged it in and ignored all my markings. The original design was 640x660, this reshuffle pushed it out to around 670x670 (I think, I haven't actually measured it).
Next I removed the track and drew contour lines all over the place to add the required features. I went with 10mm as it sounded like a reasonable amount. The original plan was in inches, but there was a lot of fudging from that anyway, so it worked out. I managed to find some 10mm polystyrene sheeting in my father's shed to cut out as a level to build up the contours. This would have been great, except for the fact there wasn't enough to do a single layer. I went out shopping, but the closest I could find was 13mm, which meant redoing all the contours. When purchasing said material I was asked if it was for a model train or Warhammer - I think the Clark Rubber staff know their customer base.

Finally with the board marked up beyond reasonable comprehension I cut out the polystyrene and built up the levels. I ran out for the last contour, so I used the 10mm stuff there which should do the job. All up I'm very happy with one day's work.