I try everytime to get solids, but sometimes you must work with joined surfaces when the objekts "super complex".
Here you can see a small tutorial about the construction prinzip.
The most parts are build like this:



Big

https://m8aj3g.dm1.livefilestore.com/y1mejL9ho5BdVV8Mc-2MMBH4GQt2hwynk8LuVtqBp4EnsRV4pKLu0s2YVgG_nl-Ag-gBCIiILItwClD1yWK0TqOvw/Tut2.jpg?psid=1