First, know when "your spare time" is. After "completing" something (or just calling it quits for the day), go for it. Doesn't matter what gets "built". Just knowing you've done something enjoyable for yourself, whether it's tangible or not, is an accomplishment in itself. Second, if serious about building something others can benefit from, create that list...a plan in action...whatever you want to call it. Then you can measure your progress until it's DONE. Good luck.