On the way home from the flea market with the bar stools, aka soon-to-be-repurposed-desk-legs, I stop by the hardware store for a pre-cut tabletop...to the tune of 15 bucks.
Once home, I lay the tabletop on the ground and position the bar stools seat-down towards the ends of the top, making sure they aren't visible. I also check to make sure my chair will fit in the space, which it will. Draw a circle around the bar stools to outline their proper placement.
Pre-drill screw holes into the bar stools so they won't crack when they are screwed to the tabletop. Before final placing the bar stools, use some wood glue (I love gorilla glue) on the seats for extra holding power. Place the seats in the circles and screw the bar stools into the tabletop - I used 5 screws per barstool.