The basic Tamil poetic unit is the asai, which can be can be monosyllabic (ner) or bisyllabic (nirai). 1-4 asais make a cheer, though 4-asai cheers are not used in venpa poetry.
Four cheers make a foot or 'adi', which is the line of the poem. A a venpa poem is one where the last line is just 3/4th foot (eetr-adi). An eetru-cheer is a truncated cheer.
1-asai cheers: These can only occur in the end, and that too they must be either a naal (1 long vowel) or a malar (2 short vowels).
2-asai cheers: 4 types are possible (nerner, nernirai, nirainer, nirainirai) and all are allowed except in the last cheer. The last cheer (which is truncated) must be either naal-short (long-short) or malar-short (short-short-short).
3-asai cheers: Though 8 types of asai combinations are possible, only the nirai-X-ner cheer and ner-X-nirai cheer are allowed. Both long and short vowel ners and nirais are allowed.
Three rules govern the assembly of cheers:
a)X-ner must be followed by nirai-X or nirai-X-ner.
b)X-nirai must be followed by ner-X or ner-X-nirai.
c)nirai-X-ner must be followed by ner-X or ner-X-nirai.
I hope with these rules once can make up an English venpa quite easily.