Need help making an incubator Please?

What you really need is something that will keep a constant temperature with 70% or higher humidity. Sphagnum moss is the best type of moss to use or you can use sterile vermiculite or perlite (moistened). You need to look up the temperatures needed to incubate red eared sliders. You can put them in a box like a plastic tupperware container with very small holes in the sides and then place this in a styrofoam cooler to keep temps constant. You need to find somewhere to keep them that remains at a constant temperature within the range needed for the species. If nowhere in your house is appropriate you would have to use an artificial heat source. Don't put them in the sun or outside because this could easily kill the eggs with temperature fluctuations.