please help

[al0ss4w0rds.livejournal.com]

im still a beginner knitter but i have almost finished my first purse, its all out of my head with no pattern at all, and now im stuck..i dont really know how to go about doing the strap. ive seen some patterns saying that you should cast 100 something stitches, then knit a few rows, then cast off. but i want my strap to be really long, and im using very chunky yarn. so i dont really know what i should be doing. the casting on a lot wont work, because i will run out of room. i was thinking perhaps i would cast on about 7 stitches, then knit the length of what i wanted, then line it with some cotton fabric. i was hoping for it just to be a sturdy strap by itself, but i dont want it stretching any being down to my ankles. please give me any suggestions!