Problems with map 7 - dragon workers cant build

Problems with map 7 - dragon workers cant build

At the beginning of map 7 my little yellow dragon drops an egg and a dragon worker appears.

But this dragon worker cannot build anything except dragon roosts. To complete this map I have to build a couple of sider buildings - how can I do that?

1. The dragon which spawn dragon units appear after a short time around th edragon roost

2. Use Metas brood egg to breed a worker

Meta does not have an egg in level 7 when i play the campaign. Hence, it is impossible for me to complete mission 7.

Is there anyway to solve this?