Extension Pack D Each of the six Extension Packs builds upon the previous pack, until the stage is reached that the full TrakMat layout is completed. Starting out with a Hornby Train Set, the next purchase would be Extension Pack A, with each subsequent Extension Pack being dependent on the previous one being purchased. The Building Extension Packs enable the newcomer to the hobby to build up a range of useful buildings and structures in an ordered way, the packs featuring platforms and station buildings, trackside structures, goods buildings and signalling equipment. Once a layout is completed by using the Extension Packs, it can simply be enjoyed or used as a springboard into the wider world of railway modelling Suitable for ages 14+