Sonny I have done this on the shop and my garage and my brother in laws 3000sf shop.... The kits from Lowes are good but you will spend more time in prep than anything else... Go buy some muratic acid and made sure you acid wash the floor at least twice... I would recommend 3 times to get it good. If the floor has oil or any debris on it then you will have flaking later. When you wash it make sure you scrub it too with a shop broom, you really need to get all the bad stuff up..... Rinse it all good twice then let it fully dry, wait the extra time and let it get all the water out of the pores of the concrete.
What makes epoxy so good is that when you put it down the first time it will go into the pores of the concrete and bind to it giving you a great base. If you have oil or debri or water is in the pores then the epoxy cant stick....
Once the floor is clean and dry its as simple as rolling the floor with a paint roller, you just have to make sure that you put it on evenly.... If you can swing it do both sides at the same time or you could end up with two different shades of the same color.
Cap