must be simple not hard to make.

Just buy one, i dont regret buying mine.

I use to take a plastic sandwitch bag and fill it with some lube and jerk off. Feels great and easy to throw away after cumming.

pringles tube, 2 sponges and 1 latex glove.

http://fleshone.com/homemade-sponge-fleshlight-tutorial/

For many years I would take a towel and roll it to tube . Take a rubber glove put in one end stretch cuff over towel . Pour some lube in and slide your dick in . You can either Jack it off or lay in bed put under a pillow and lay on it . Feels as good as a pussy to me

That's called a Fifi. And it works very well.