I worked at cincinnati glass block a few years ago. go to home depot they sell glass block. any idiot can do this if you have general construction knowledge. they sell the mortar too. most glass block companies use silicone instead of mortar now. not sure if home depot sellsyjr proper silicone for this or not. they should. you want clear. measure the opening and bring it with you. bring a tape measure. the blocks come in a few different sizes. sometimes you have to go with a few of one size and one of another to get as close as possible. to assemble the blocks lay them down on a flat surface and glue them together. silicone is so much easier for this job. let it set up for a day or two. and it's ready to install. if you use mortar that's a big time mess and undertaking because you have to space the blocks etc to get a even look. you basically do it just like a brick wall. they also of course sell the mortar that goes around the window. it's not the same as the mortar you assemble the glass block with. buy a foam brush too. you will need to mix it with water and you can use whatever you want to fill the opening with. I often just used my hands. pad the window up at the bottom with cedar shims. you want the window centered in the opening for the best apperance. now use the other shims to hold the window tight in the opening. cut the shims back with a razor blade as flush as you can. now you can pack the gap with the mortar. they also have a bag like a cake maker uses for icing. they come in handy but not really needed for just one job. after you pack the sides, top and bottom scrape it flat with a trowel etc. then dip your brush in water and use it to finish the mortar. if you lived in cincy I'd do it for about $80 not including the materials. you'll end up paying about $200 I would guess for a glass block company to do it.