i Love making Bargello quilts! i've made about a dozen of them- i have enlarged them by increasing the sizes of each individual strip---turned out ok----i have enlarged by increasing the amount of fabric/number of strips and continued the pattern---it took a few pages of graph paper & some (thinking) but it worked out pretty well-
i've also redesigned the pattern to include new (inner) borders - as in part of the main design---border---more of the design outside the border- another border ect...that one is probably the coolest-
the easiest way is to either buy the pattern in the size you want or add outside borders---
what ever way you go- bargello's are fun & can really allow you to be creative- have fun with it!