No matter what canvas shop you use to build your canvas, knowing which type of fabric to use in different applications is super important.
Covers- Its hard to beat Sunbrella for just about any cover, it breathes and keeps water out. Be sure NOT to use sunbrella plus because it has a plastic coating and limits the breath ability of the fabric. Proper design is very important- if there is an area that is flat and can collect water, it will eventually start to leak. Some applications call for TOTAL water proof fabric, such as some electronic covers. If this is the case be sure that the cover has some sort of vent at the bottom or you will be fighting mildew problems.
Bimini Tops- Here there are a few more choices. As a go to fabric I prefer Sunbella, again breath ability and long life put it at the top of my list. Other good choices are Stamoid, Weblon, and SeaMark. All three are great choices for being very water proof for the life of the fabric, be aware that the trade off is lack of breath ability especially if the bimini has a full enclosure and if the fabric is a light color. I recommend staying away from "off brand" fabrics here- biminis take a beating from the sun and since a small percent of the cost of the job is the material (ie its mostly labor) it doesn't make any sense to skimp here.
Enclosures- For the "soft vinyl" (aka isenglass) you get what you pay for. Be sure the glass is a pressed polished sheet (NO roll goods). The brand we have had the best luck with is Chrystal Clear (by Strataglass) It is reasonably priced and does very well in the Florida sun. For the thickness we almost exclusively use 40 guage (unless a customer asks for something different) . It seems to form the curves better and the thickness decreases distortion. The ultimate in enclosures is the Hard Window (these are stiff panels but can bend around a pretty tight radius, have perfect clarity, and zero distortion- its more like a car windshield than a boat windshield). The material we always use is Makralon AR. We have been making hard windows for 20 years and this material is by far the best we have used. Many shops are making these panels since we have all figured out how to sew them in, but not all shops are aware of how important using the correct material it. If the wrong material is used it can be brittle and/or turn yellow in less than a couple years. As a side note, I always recommend buying a windshield cover to extend the life of the windshield.
Exterior Cushions- Closed cell foam or a flow through foam (there are several brands available) are the only choices, do not use regular foam here it will always be wet and a moldy mess. For the fabric I highly recommend using a coated yarn fabric (brand names such as textaline, phifertex, awntex) and be sure to use the tight weave because the loose weave (you can see through) lets the UV rays eat up the foam. Sunbrella is a poor choice since it is much more difficult to keep clean (unless you go with a dark color, which will be terribly hot to sit on in the summer).
Interior Cushions- A good acrylic fabric is a must. Most people think since it is down below it can be a standard interior fabric. Most boats get a lot of sun down below so a cheap fabric will fade very quickly. Also, there will be people in wet clothes, spills, and very high wear on this fabric. I try to steer people to the Sunbrella line of furniture fabrics, I have used it personally in my house (white couch with two kids and two dogs) and it is phenomenal fabric.
This is just a few of the more common products, if you have a specific question please let me know in the comments below.