Group projects are hard, especially science projects, so here's a list of things that any person in a group project should take into consideration. - a High School Senior with Much Experience in the Way of Group Projects.
You may not have enough or you may have too many, but be prepared to go shopping for materials. Try to make a list of all the things you need (especially the things you are required to have) and get everything all at once.
2. Uncooperative Schedules/ Groupmates
At the beginning of the project, try to coordinate a place and times to meet where at least two of your group can get together to work on the project. Of course, sometimes you just have uncooperative groupmates that can never meet or simply won't make the effort to show up to a meeting. Without creating a clear schedule, mistakes can easily be made.
Try to plan with your entire (or at least the majority) group present, so that everyone has a clear picture of what's expected and what's going to be done. Planning is the most important step and should be done first. Without proper planning, a project could easily be doomed to an all-nighter right before the due date.
You have a list of the needed materials, now you need to go shopping. My advice is to take at least one other person from your group and to try to get as much as you can at once and as cheaply as possible. You want to try to avoid multiple shopping trips because they take away time that you could be spending on the actual construction.
5. Plan A, B, C, D...
Yes, it is probable that your first idea either wasn't done correctly or simply doesn't work. In preparation for this, have a backup plan, a backup plan for your backup plan, and a backup plan for your backup plan for your backup plan.