"I came to the shop at nine o'clock."
Translation:Des i i'r siop am naw o'r gloch.
I tried 'mi wnes i ddod...' but was corrected with 'mi ddes...'. should I only use gwneud with normal verbs and not the irregulars?
Peole do tend to use the short forms of the common irregular verbs simply because they are so frequent and so easy to use.
If you ever look at examples of early literature written in Middle Welsh you will find examples of earlier versions of these irregular verbs. Some of them in Modern Welsh have come about through the merger of a couple of older verbs, and then frequent spoken use has led to some contracted versions becoming adopted into the common 'standard' language, while others persist only in dialect forms.