Structural modelling on your railway will be governed by the area in the UK, and in the case of buildings and surrounding structures, the railway company. Each of the railway companies had there own design styles and colour schemes for their buildings. This is also true of the surrounding structures, some of them being there for many years. With a modern image layout there will be a mix of old and new styles. Buildings were constructed of different types of materials, railway buildings being of either stone or brick construction, whereas the surrounding structures may vary and in some instances constructed of a mix of both.
If you are not able to visit the area you intend to model then I suggest you do some research through either the Internet or books. There are many books on the different areas of the country and some focussed on times gone by. Some of the railway history books contain plans and these can be enlarged or reduced to your chosen scale. I was lucky as where I worked had an excellent photo copier which I used for my plans, admittedly you are limited to the area/size but it is very easy to paste or tape them down onto a board. I always do this as it is handy to have a drawing you can visually check your model against. I transfer the dimensions on to my chosen medium to build the basic structure, usually 4mm. good quality plywood. In transferring the dimensions always allow for the detail sheets you will add to finish the outside of the structure. In 4mm scale Wills Kits produce embossed plastic sheeting in various types, Slaters Plastikard and South Eastern Finecast produce ranges of embossed sheeting to cover 4mm and 7mm which comes out much thinner. You may even still be able to get Howard Scenics embossed card sheets, but there are other companies who produce brick and stone paper finishes.
Many companies produce parts for the scratch builder, York Modelmaking will produce parts specifically for your project, and the likes of Ratio Models, Smart Models, Scalelink, Duncan Models, Langley Models and S&D Models produce many detailing parts from window frames, doors and chimney pots to brackets and finials for your railway buildings. You can construct your models as detailed as you want, there are many suppliers out there.
Probably some of the best exponents of scratch building are the modelling team at Pendon Museum. All of their subjects are meticulously researched and the techniques they use are well documented, in fact there is a book from Wild Swan Publishing called ‘Cottage Modelling for Pendon’ which is a fascinating read giving much information on the techniques they employ.