A friend of mine asked about my experience in adding tieouts to my Chinook 12' x 14' tarp to assist him in purchasing the best tarp for his needs between the Chinook 12 x 14, the Guide Gear 12 x 12, and the Guide Gear 16 x 16. I figured I'd post here to assist others possibly.
No biggie to sew some tieouts on it (even hand sewing them probably wouldn't be that tough). You could, instead, use Grip Clips if you don't want to sew at all (which I did for a year before I got my sewing machine). I would recommend sewing tieouts or using Grip Clips instead of any grommets (the ridgeline attachment points are grommets on the Chinook, replace them with webbing tieouts or Grip Clips).
I added 2 tieouts for the ridgeline and 4 for the corners (as the tarp has tieouts that do not lend themselves to being used as a hammock tarp).
I used the dimensions of a Superfly as somewhat of a guide (IMHO a good starting point for dimensions for a 4 season tarp).
With the Chinook 12' x 14', if you want the same ''livable space'' as a Superfly (91'' corner to corner), you'd have to sew tieouts at 37.5 inches in from the tarp's corners. This would only leave you with 37.5 inch doors (compared to 41'' doors with a Superfly). This would mean you'd need to pitch the tarp in a more aggressive A-frame (granted, not much more than the Superfly as you are only losing 3.5 inches per door) in order to get the doors to close fully.
You could sew the corner tieouts at 41'' in from the tarp corners so you could have a wider A-frame pitch (mimicking the door length of the Superfly); you are, however, losing "livable space" though (84'' compared to 91'' with the Superfly).
I went with version 1, maintained the same "livable space" as the Superfly and still had decent-length doors.
(edit - going off the measurements in the picture from another forum member in second post below)
If you would do this with a Guide Gear 12' x 12' tarp and you want the same ''livable space'' as a Superfly (91'' corner to corner), you'd have to sew tieouts at 20.5 inches in from the tarp corners. This would only leave you with 20.5 inch doors (compared to 41'' doors with a Superfly). This would mean you'd need to pitch the tarp in an extremely aggressive A-frame in order to get the doors to fully close. Not preferable IMHO.
If you want the same sized doors as the Superfly (41'') you would only have 50 inches of "livable space", much too small IMHO.
(edit - I am assuming these dimensions I have estimated for the 16 x 16 have to be smaller as the actual dimensions of the 12 x 12 are quite smaller as illustrated previously. I have not personally measured the GG 16' x 16' tarp)
If you go with the 16' x 16' Guide Gear, it is, I'm assuming, much easier to end up with desirable dimensions IMHO compared to the 12' x 12' Guide Gear .
If you go with the 16' x 16' Guide Gear tarp and you want the same ''livable space'' as a Superfly (91''), you'd have to sew tieouts at 50.5 inches from the tarp corners. This would leave you with 50.5 inch doors, even longer than the SF doors with the same 91'' "livable space".
If you want the same sized doors as the Superfly (41'') you would have 110'' of livable space (slightly more than the 91'' Superfly).