One of the biggest problems with sno pushers is training the operators NOT to use down pressure. The pushers are for pushng snow, not cutting snow pack. The skid plates on the side pieces effectively stop the down pressure from being effective. On skid steers, use the float position.
As for how long it takes to make one ?? Depends on just how good a fabricator you are. If you have a mold board, you'll put in around $500 in materials. It now takes our guy (and he is very good) about three days to fab one up. And, we are using flux core wire on a semi-automatic feed welding unit to speed up the welding process. Larger ones take much more time and you need the ability to flip the unit around to be able to flat weld it instead of trying to weld verticle up or overhead.
I also think you're making the process too complicated. The pushers don't use hydralics and they hook right up to the bucket. 5 minutes (tops) to hook it up to the loader, less with a bobtach arrangement for skid steers.
Extending a 7.5 ft. mold board out to 14 foot isn't something I'd suggest (from experience). LOTS of addditional work in beefing up the rear of the unit with channel (5" minimum). We built one 14 footer and one 20 footer ourselves. Most of the ones we built were 10 footers using old street plows. On the larger ones we used old diesel tanks that were 24 ft. long. Cut the moldboards out of the steel tank. Got two tanks for nothin and made a bunch of pushers out of them.
Incidentally, we just put a urethane edge on the 14 footer we built (and refirbished recently). The urethane edge works real well. We did have steel, and that caused problems when the operator hit a manhole or went over in imperfect parking lot. You'd be amazed at how well them things peel up blacktop !! We're going to change over all the ones we built from steel to urethane.
All in all - for larger ones.... buy them. From experience.... it's less aggrivation.