Leaving anything open isn't worth the risk
If you have a proper upright wheel(which you absolutely do need)then that is an easy enough escape route if a hamster gets the chance.Hamsters also climb out by climbing onto water bottles,and no matter how high you position something they can always pile substrate and other things underneath in order to gain access.
Even if you don't have other animals in your house,there are many other risks including toxic household substances.Hamsters will not hesitate to at least nibble on most things,even if it may kill them
Making a lid only requires mesh as Drago mentioned and a wood burning knife(or another similar tool).Making a lid with wood is unreliable at best since it won't be as secure,so I'd just avoid doing that(plus it costs more to get tools to put a wood lid together,if that matters to you!).