supporting tomatoes?

I have seen on telly numerous times tomatoes being wound around string dangling from the greenhouse roof but they never show how it is attached to the roof ? can any one give me any tips ?

Fix canes or wires across the roof and drop the strings down to the tomatoes.

like this perhaps

If you haven't any fixings already there than use some cropheaded bolts with large washers to tie up to, or  fixings like these
http://www.twowests.co.uk/product/bolts-nuts-and-rings-pack-of-10

I make a bamboo cane lattice affair starting with sticks in the pots and string the horizontal ones on to them.
I then tie the cane support to the metal greenhouse window supports to hold everything upright.

I always use new canes each year though, in case of spores from infected toms have made a home on them.
I use the old canes then for something else like sweetpeas or beans.

I have a local shop in Cornwall that sells canes for between 2 and 16p each dependent on size so not much cost there.