Last evening, I finished off a storage bag for my folding Sawvivor saw (draw string top, pocket for spare blade, nylon that I treated with silicone spray to waterproof).  Now I'm looking to take on something a bit bigger ... a 10 X 10 Silnylon tarp.  I have some silnylon yardage on order, but I had a question (or ten) about construction. 

My aim is to keep the total tarp weight under 1 lb.  The 1.1 oz (1.3 oz after silicone treatment) silnylon material comes in at about 9 oz.  The plan is to use flat felled seams to join panels and a "rolled" seam for the edges.  Are those the best options?  What seam allowance would you use?  I'm thinking 1 inch.  Do you have a preferred light weight tape material that you would recommend for tie-outs?  Would you "double" the tie-out points with an extra patch? Would you place tie-outs at 2 foot intervals (at least those opposite the ridge-line) or do you prefer 2 1/2 foot?  Would you use nylon or polyester thread (and what weight)?  Other than the ridge-line, would you re-seal sewn areas?

Any other design options you would consider for pitching versatility?

dd