It would be great if we could have vlan tagging support when constructing with packet builder. vlan tag is just another 4 bytes After the source Mac address before Ethernet type (nothing else).
Those 4 bytes are
xxx. .... .... .... = Priority:
...1 .... .... .... = CFI
.... xxxx xxxx xxxx = VLANID
(see
http://en.wikipedia.org/wiki/IEEE_802.1Q) frame format.