I love the ease of PicMonkey for creating collages, especially for things like Facebook covers. They even have a Facebook cover template. There’s not a Google + template but it’s easy to create one!
I created my Google + Cover using one of the Pinter-etsy templates with custom dimensions.
Since Pinter-etsy is a premium template I played around with L-egant, a free template, too. (Just to show there are options even if you’re not a premium PicMonkey user!)
At the bottom of the page just click on the lock to unlock the proportions and change the dimensions to 2120 x 1192. PicMonkey will do the rest.
You can play around with whatever template you choose, adding more images, adding or removing space between the images and rounding the image corners.
PicMonkey has a selection of swatches you can use for blank spaces in your collage. You can even upload your own. To add text just save your collage and then use PicMonkey to open the collage in the editor.
Once you’re happy with your cover photo just open Google +, visit your profile, click on “change yours now” where your cover image is located and upload your collage!
When you’re bored with your cover just create a new one and click “change cover” on your profile!