I’ve found two tools which can help you in the respect of building things in SL:

• A terrain file editor for OS X only named Backhoe. Looks pretty good and snappy to me on the screenshots and if you ever get your own island it looks like a very good way to make a terrain file to give to the Lindens.
• A script to be able to rez objects made in Maya in Second Life called „Maya -> Second Life: Beta version.“ Maya is one of the best professional 3d editors around there, for many in the industry the 1st choice actually. So how does itwork? It gives you in Maya a new tool box with the prims of SL and the same options. You basically built your shapes in Maya, when you’re finished with it, you export it to your clipboard. Then you login to SL, equip one object with the rezzing script, load the clipboard’s content on a notecard into that object and let it rez the imported structure for you. Then you can texture it and so on and on. That’s it, basically.