So the first thing you need to do is get all your tiles printed out onto 110lb cardstock. I went to Staples and brought my own paper, so it was $.49 per page. If I had it to do again, I would combine more tiles per page to save myself money.
Next, find self-adhesive rolls of magnet backing. I went to Hobby Lobby and got 4 rolls for $9.99 each. You can probably find them online for much cheaper, but I was in a rush.
Get a decent pair of scissors.
Cut out all your tiles and corridors leaving a little bit of edge remaining. I ignored the white walls that separate the tiles, so I will have gaps, but because it will be on a black-painted steel plate, It should look fine.

Lay out your tiles to get a good idea of what will fit and try to make the best use of your space so you don't waste magnet. If you do need to have wasted space, leave it on the edges so you can line those up later and maybe combine them into a smaller tile backing. The flat edges line up great for this.

Peel off the backing and lay out your tiles again.

Cut your tiles out to the size you need.

Here is the completed board. I was playing with the center area to see about using tiles for the HQ25th Anniversary tribute quests on it as well...

Here is a look at what I still need to do to make a fully compatible HQ25 magnetic board.

I hope you all like it!