Visited various shops in Kilmarnock (my home town) to purchase block-board base (£24.31) plus a selection of tools.
Performed the ritual garage clear-out to make space for the build and drafted the plans onto the block-board. Note that although Ron Champion correctly recommends that you don't use a chalk line to mark the centreline, I would recommend that a string line is stretched between two centred nails to establish a few centreline marks which can then be joined up with a long ruler. Don't use the block-board edge as a reference as it is not likely to be true. I did this initially and then looked down the line by eye only to find it was not straight, even though I was very careful with the marking out.
On the subject of marking out, follow Ron's advice on getting a LARGE set square and LONG ruler. I got the 24 inch square and 40 inch ruler and it makes life much much easier! Both came from the Focus do-it-all shop for not much money.