Thank you, gentlemen.
Robert, there are a few plugins that only work with the pro version of SketchUp but that's because they utilize native pro-only features. The vast majority of them will work in the free version as well.
As for sources, there are several good ones out there. The
Extension Warehouse and The
Sketchucation Plugin Store are the two major sources.
While there are a lot of useful plugins out there, it is a good idea to learn the native tools first. I've lost count of the number of SketchUp users who ask about a plugin to do something that can be done natively. Last night I had a conversation with a fellow who was trying to make a window he'd drawn shorter. He'd cut out a section from the middle and was trying to join the top and bottom parts back together. He'd used a plugin to make the cuts and was looking for a plugin to help join them up. The joining only required the use of Intersect Faces, a native function, but he could have saved himself a bunch of work and time if he'd only used the Move tool to move the upper portion of the window down.
As far as installing plugins goes, there are a couple of things to be aware of. If you are still in the dark ages using SketchUp 2013 or earlier, and you've never installed a plugin, you may need to go to the Plugin folder and set permissions to allow you access to it. Win7 and MacOSX both locked down access to folders in the Program Files and ~/Library/Application Support directories. If you are keeping up to date, SketchUp 2014 has the Plugins folder located so you don't need to change security permissions.
There are several different file types that plugin files might be downloaded in. What you do with them, once downloaded, depends on the file type. It also depends on the version of SketchUp. For files you would get from the Plugin Store, I would highly recommend that you first install the
Plugin Store extension. This will automatically and properly install plugins into the right location. With SU2013 and SU2014 you can access the Extension Warehouse from the Window menu and also automatically install plugins.
FILE TYPES
If you download plugin files but aren't using the previously mentioned tools, here's what you'll do.
.rb --Move the file from the location you downloaded it to into the Plugins folder. You'll have to restart SketchUp to get it to show.
.zip -- You can extract the contents of the ZIP file to the Plugins directory but it is imperative that you maintain the file structure in the ZIP file. The Windows unzip utility is notorious for destroying the file structure in the process of unzipping. Use 7-ZIP instead.
If you are using SketchUp 8 M1 or later, a better way is to change the extension to .rbz and follow the steps in the next section.
.rbz -- Open Preferences/Extensions (under the Window menu on PC and under the SketchUp menu to the left of File on Mac) and click on Install Extension...
If you haven't got the Install Extension button on your SketchUp 8 installation you are really living in the dark. You are still using the first release of SU8. Navigate to the location where you saved the file, select it, click on Open and then OK. the file will be installed. Depending on the extension you may or may not need to restart SketchUp to get it to work.
If you haven't already done so and you aren't limited by your operating system, you really should be using SketchUp 2014. Before you bother installing any plugins, you ought to get current with the program.