Translation:Do you think that this is Megan's work?
Is this the usual pattern you would use in Welsh to ask such a question? It looks quite complex...
Yes, it is a commonly used pattern. It is just two basic clauses joined by the word mai. It matches the equivalent pattern in English.
An alternative word arrangement would be:- 'Wyt ti'n meddwl mai hwn ydy gwaith Megan' which would be closer to the English translation:-
Wyt ti'n meddwl = do you think
Mai = that
Hwn ydy gwaith Megan = this is Megan's work (lit:- this is work of Megan)