Deciding on magnets
With an N42 1"x1/8"x1/8" magnet we are getting a bit over 2 lbs. At $0.74/piece, you can make this clamp for $2.96. These are a bit weak (but can still work) with tiles, but would be wonderful with thin strips of wood, or smaller parts like the docks construction kit pieces.
With an N42 1"x1/8"x1/4" magnet we are getting a bit over 2 lbs. At $1.26/piece, you can make this clamp for $5.04. I recommend this set for most tiles. They are strong and will hold the tile while you glue.
With an N42 1"x1/4"x1/4" magnet we can get a bit over 5 lbs. At $2.14/piece, you can make this clamp for $8.56. These monsters are great, but on normal tiles, they are so strong they repel each other so it makes them a little harder to use on something 2 inches x 2 inches like most tiles.
If you want to go even stronger, you can get N52 for $2.75/piece for $11/clamp. I estimate these should give about 6.25 lbs of clamping force.
Thing is, testing these with my tiles, I think even the cheapest option is still useful, but the stronger ones are even better. And if what you want to glue is thin wood, the lighter touch is probably preferable. I personally made two of each strength.