This site explains how to draw railroad vehicles for Transport Tycoon. I suppose you know the game Transport Tycoon, so I'm not going to tell something about that game.

Some great people made the TTD Patch, which gives the possibility to add custom graphics to TTD, like that's done with the DBSet. This site explains how to draw train graphics. It contains info which you need to know, and has a number of tutorials where you can draw railroad vehicles from scratch step by step. I (a graphics artist) thought it would be useful to have such a website.

Although this website only shows tutorials of drawing railroad vehicles, it might contain useful information for artists who wants to draw buildings or other types of graphics for TT.

REVISION
These tutorials only explain the basics and will get you started. After these tutorials you'll have to develop your own style, and keep improving that style (which can take years of practise). My own drawing style has improved a lot since I made these tutorials, so the sprites shown here are not too amazing. Some parts of these tutorial pages may be outdated, and some revisions were made without updating the rest of the page.