An editor, that can do any kind of wonders in real life would be really nice, but I haven´t found it yet. Fortunately for Civ 3 and especially C3C you can create wonders with every C3C standard editor, even with the editor, that is included in Civ 3 Complete (now the most familar version of Civ 3 and C3C). If you open a biq with the standard C3C editor and klick on the register for improvements and wonders, you have the options posted in the screenshot below:
I have marked in a red box the section that is important for assigning a building to be a normal improvement, a small or a great wonder. You only have to klick on one of these buttons to do the selection.
That forum is for common questions about modding Civ 3. The forum you are posting now, is for special modding projects, per example creating a new Star Wars Scenario or a WW 2 scenario with a lot of modding stuff that should be coordinated.