The Hollywood couple are set to tie the knot in August but they have yet to find a venue that they like and will be big enough to hold all their guests.
A source told Us Weekly magazine: "It needs to be in California and offer plenty of room! It will be a big wedding. They have lots of people they want to invite."
However, Jessica is getting plenty of help from Justin's mother, Lynn Harless,who is giving her future daughter-in-law lots of advice on planning the big day.
The source said: "She's helping Jessica with every little thing."
But one thing Jessica - who split from Justin last year only for them to rekindle their romance before Justin popped the question - has decided on is the designer of her dress.
