My steps, roughly:
-- dug a sand pit about 1.5-2.5' deep along the house - grade slopes away from the house (by hand, so no formal expense)
-- built the enclosure around the pit and attached it to the house side - 4x4 posts, roof boards, shade cloth, UV-treated tarp on top, insect netting for walls - no expenses included in the numbers above as these are not directly related to the tank construction
-- one 50' wall is the house wall, so built two 15' sidewalls out of wooden posts and doubled up 3/4" plywood, all pressure treated of course
-- built the window, 42 feet x 43 inches to be exact, joining five ~9'x43"x3/4" acrylic panes with four 2' wide posts (posts are outside of the tank) made of laminated sheets of acrylic, posts are 7' tall (~1/2 dug in ground, ~1/2 of the post height is above ground); glued 2'x43"x1/2" panels to each of the 4 joints on the inside, plus 6" wide strip all around the remaining perimeter of each of the 5 acrylic panes inside and out, top and bottom; plus two 3" wide acrylic strips along the top inside and out and a 6" wide acrylic top (to make a T top) along the entire 42' length; the glue is weld on #40 at $550 for 4 gals before shipping from Interstate Plastics, California, took 16 gals; watch and listen to the video above
-- all acrylic is from Craigslist, all cell cast - fish tank appropriate, NOT extruded
----- 9'x43"x3/4" five, $950 all
----- 7'x5'x1/2" eight, $400 all
----- 8'x4'x1/2" five, $600 all
-- attached 60'x20'x45 mil EPDM rubber liner to the window -
----- cross section: window | Dow 795 | liner | 3" wide acrylic strip, 1" thick
----- the 3" strip runs entire length and sides, one piece, made out of 1/2" acrylic
----- the 3" strip compresses the liner and Dow silicone with 1/4" stainless steel 316 marine grade bolts every 4.5", about 100 bolts
----- the vertical sides have no bolts but are screwed to the wooden side posts with stainless steel 6"x5/16" screws
-- dressed the sand pit, made an ~45 degree angle at the window to eliminate blind spot below the grade - the window only shows top 43" of the overall 4'-4.5' depth
-- laid down make shift liner underlayment - 4-5 layers of high quality, thick, used greenhouse plastic, waste scavenged from my neighbor who runs an orchid nursery
-- spread the liner
-- water tested, holds water
That's where we are at. I am fixing the liner to the top perimeter and building a wet/dry filter for the tank that will run on ~7000 nylon mesh pot scrubbers. Projected flow - eight to ten 5000 GPH pumps.