If you want to make a simple girder bridge like that one it really is quite an easy solder project, remember everything is built as right angles at 90 degrees, also everything is a mirror of itself so once you have one side made up you just make another. The way I work is to draw out the design with measurements showing, then cut the main pieces of brass, before soldering anything together I always scribe lines which act as indicators for where other pieces will need to go. If you don't do this at this point then it will be near impossible once you start assembly, details such as the top gusset plates of the girder beams or the strengtheners on the girder webs will not look in proportion otherwise. The best advice I can offer is always check your brass work for true and level against a flat stone, I use offcut pieces of conglomerate marble as used for kitchen worktops as a flat stone because they are heavy and so won't move easily and they also have a polished surface with helps. Remember too much heat will distort the brass so when making sub assemblies always start in the centre and work outwards and use a heatsink to dissipate any thermal build up. The other thing is don't try to be over ambitious... keep the project simple to start with. Any problems just fire in a question and either I or someone else will help with advice. Best luck Steve.