If you are considering doing this yourself, I highly recommend you buy this.
This little tool made all the difference in the world. I can not live with out it. I bought mine at Michael's with a 40% off coupon. Soooooo worth every penny, even if I had paid full price. Keep in mind that you can't use it when you get as close to the ceiling as my pictures are. You have to eyeball it when you get that close to the top.
I love how my gallery wall turned out. I just sit and stare at it while I sip coffee in the morning. I also look at it while drinking a beer in the evening. It is a multi-beverage viewing wall...
Come on over and have a beverage with me and enjoy my gallery wall. Emma Jane said she feels like a real artist now.