"Ozymandias" by Percy Bysshe Shelley is a poem that utilizes a slightly irregular version of the sonnet form.
The rhythmical pattern of the lines is iambic pentameter. To unpack this, we describe poetic lines in terms of two things, the smallest repeated rhythmical unit of the line (called a "foot") and the number of times the foot is repeated in the line. Shelley's poem uses an iambic foot, meaning that its basic pattern is that of an unstressed followed by a stressed syllable. This pattern is repeated five times in each line, and therefore we refer to the meter as pentameter, a word meaning five (penta-) measures (meter).
As the poem is comprised of fourteen lines in a somewhat regular rhyme pattern, it is a sonnet. However, the rhyme pattern is not completely regular. The first two stanzas are irregular open quatrains (abab acdc), appearing to follow the pattern of an English sonnet, but the final six lines appear a variant on the sestet of an Italian sonnet (ece fef).
Thus perhaps the best description is that this is an iambic pentameter sonnet with a slightly irregular or hybrid rhyme scheme.
"Ozymandius" is written in iambic pentameter, which means that there are ten syllables in each line of the poem in five pairs of two, with the first syllable in each pair unstressed and the second syllable stressed.
I met/ a trav/-eller from/ a dis/-tant land/
The first eight lines are the traveller's description of what was seen in the desert, recognizing the artistic skill that had sculpted the "frown and wrinkled lip and sneer of cold command" with great skill. The final six lines point out the irony of the great power and majesty claimed by the figure that had been portrayed, now a "colossal wreck, boundless and bare."
The rhyme scheme is the trickier element in the analysis of the poem's structure. Shelley uses a very complicated interconnection of the rhyming words at the end of the lines to emphasize the discontinuity and irony contained within the poem's story. The rhyme pattern can be described as being "abab acdc ece fef".