Table with shelf underneath -expansion?

[Brian Penning]

Been asked to make a small table 27 X 27 with a shelf underneath.
Obviously will attach the top to the apron with allowances for expansion but not sure how to handle the full size shelf expansion that will be mounted in between the 4 legs.
Below gives the rough idea...
TIA for any and all replies

http://www.jhfurniture.co.uk/products/coffe_table_chippendale_shelf.jpg

[Chris Friesen]

Is that a solid-wood top? It looks like there's a mitered border around it...how were you planning on handling expansion there?

In any case, you've got a few options for the shelf, the obvious ones are to use plywood with solid edging, breadboard ends either tenonned into the legs or just let into notches as shown in the drawing, or diagonal stretchers with the top fastened to them and undersized enough to allow for expansion.