If you do have a top fabricated, then here are a few comments and photos.
We purchased our Islander with the Vista top and had a hard top made locally (S&S Marine in Norfolk) about six months later.
We had a top made with the same basic dimensions as the factory top, but based on comments from a lot of GW owners, we had the back frame located at the aft end of the top. This allows the aft curtain set to hang vertically, instead of the usual angle, and permits crew to be inside the enclosure behind the pilot seat or the companion seat. See this shot:
Since we don't have the large bag for lifejacket storage, and our electronics box is deeper but not as wide, we had a lot of room for rod storage. There are now TEN (yes, 10) sets of Lee rod holders up there, and we can store seven-foot rods on the sides. Your top will be smaller, but you can get a lot of rods up there.
Enclosure made locally also. Note that the front openings are upside down "D"s. These can simply be unzipped and allowed to hang inside, or they can be rolled up and fastened at the bottom. The side openings do not roll - they swing up and are fastened with two post and button fasteners each. Even swing up with the rods in place. This prevents a lot of damage to them, it is much faster to get them up when all you want to do is reduce windage for a docking evolution... Another photo:
Grab rail down the center was suggested by a friend in 2006. I drew up a simple plan and had it made by S&S Marine. Cost was $107, including backing pads for the top side.
Cost for the top in late 2002 was about $3600, including welded pads for the Taco Grand Slams, cockpit lights and four Lee rod holders. The enclosure has 30-wt Strataglass, and cost about $1800.
Brian