You should always make a model of the tent you propose to construct, first with paper, to scale, so as to get the proper dimensions, and then with linen, with string and poles complete, to see how to cut it out in the right sizes. Afterwards, you can proceed to make the real, article.
This, again, is best done by cutting it out in newspapers pasted together and spread out on the floor. These paper cuttings then serve as "patterns," on which you can cut your canvas without wasting any of it.
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THE MATERIAL.
The kind of stuff to use for tent making depends a good deal on how much you can afford for material, and what work you want the tent for.
Thus, if you want a very light tent for carrying on your back or bicycle, and have plenty of money, a silk tent at 4s. a yard is very nice; but probably you would like one of cheaper material, and fairly light and strong.
Lawn, made of Egyptian cotton, calico sheeting, or brown calico makes a very satisfactory tent at an outlay of 10s. or so for the whole thing complete.
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SEWING.
After having purchased your stuff, and cut it out according to the paper pattern, pin it, or tack it, all together, and see how it fits.