It might be helpful if you stated something about the size of tipi you want to construct. Also you seem to have several poly tarps with some of them fairly large. Large enough to be sewn or glued to one another to make the usual half-circle shaped covering of a traditional tipi . Why dont you just do that? Or are you trying to cover the poles with the tarps left in their rectangular or square shape?
Poly tarps are easily cut and glued together. Do a search on youtube for the term hasty hooch it will turn up about an 8 part series of videos in which Tinny of minibulldesign cuts and glues poly tarps to make a uniquely shaped tarp meant for light weight backpacking. The point is not for you to follow his design but rather to use the gluing and reinforcement techniques that he uses in the videos to make your tarps into a shape that will work as a tipi cover.
An alternative tipi like shelter you could build with the poly tarps is something along the lines of the Scandinavian laavu shelter. But build the kohta or kohten variety as used in Germany , Austria and other near by countries. Their version of the boy scouts , the pathfinders build these things in what I think is a rather remarkable design.
Basically you have a section of tarp which is close to being triangular in shape. Each scout or pathfinder carries one section. The sections are made such that 4 of them can be combined to make a cone shaped shelter which is rather octagon shaped at the base rather than being a smooth curved base shape. Alternatively each pathfinder or pair of them can use one of the triangular shaped tarps in a stand alone mode . In what they call a half-boat configuration. Its a tarp shelter which is erected in what we would call a diamond configuration or something close to it.
Go to google and do a search on the terms kohte ohne or kohta or kohten and it should turn up lots of pictures. However , most will be in german language but many pictures will give you the idea of the shape you would need to make with your tarps. The pathfinders tarp sections are made with a rather ingenious method of lacing the sections together so that 4 tarps can be connected to one another to make the kotha. However, you dont need that feature. You only need to cut out 4 triangular sections, sew or glue 3 of the tarp sections together and figure out what to do with the last 2 edges to be joinged to make a door way in and out.
Here are a few links to give you an idea of what these things look like. ( I want to mention here too that the German Pathfinder groups have a long tradition of building these things out of black fabric. Schwartzzelt , which is literally black-tent - they also combine the triangular sections with square or rectangular shaped tarp sections to built shelter which are very much shaped like Mongolian Yurts , at their national events they built quit elaborate cities out of these things. Never seen them in person , only pictures on the internet . The triangular shaped sections instead of being the walls of a tipi like shelter become the roof of the yurt like shelters. And the walls are made of square or rectangular shaped tarp sections )
Try these links :
http://www.scholl-zelte.de/kohte/kohtez.htm
On this next page you can see the name given to the somewhat triangular shaped tarp sections you would need to make - the kohta-tarp TST piece. You can also see drawings of how this same shape is used in the half-boat , boat , and full-boat configurations.
http://www.scandia-tents.com/english_techdata.htm
http://www.zeltstadt.at/service/aufstellanleitungen/zeltstadt-at_aufbau_kohten.pdf
http://www.jurtenland.de/de/taxonomy/term/13
This last link above is the first of several pages so if this idea interest you , you may want to look at the several of the pages at the above website. And of course do a google search on the terms mentioned above or new similar terms you may find. There are more link than I cared to put into this reply.
So maybe this is an alternative way to make a tipi like shelter you would want to try or maybe not. So FWIW.
D