Evening still new to sketchup and im struggling to get my stl file to export as ive designed it when i export its nothing like my design ive included the file to have a look at
pitpit.stl (3.9 MB)
Share the .skp file so we can see what you are working with.
Hi Daver its attached above 
thanks
i think its to do with my groups but not 100% sure
You attached the .stl file, not the .skp file. I want to see what you are starting from.
Oh my bad ill reupload
pitpit.skp (435.8 KB)
Instead of SketchUp not exporting the .stl correctly, it is just exporting what you’ve created but which is not what you are expecting. So the first thing I see is you have reversed faces. There should be no exposed blue back faces. If your intent is to 3D print this thing, the face orientation is critical. The blue back faces point toward the print media and the white front faces toward air.
You have a lot of unneeded nesting of groups along with some hidden ones in the parent. This can create issues.
The long walls of your thing are loose geometry within a group that also contains the ends a group for the ends and a nested group for the bricks so even after you fix the face orientation, those walls won’t be recognized as printable in the slicer.
Your model needs a lot of rework. There’s no need for all of the nesting and no need to create the end walls as a separate object from the long walls. I’ll see if I can fix it for you but it’s such a mess I expect it would be easier to model it from scratch.
hi dave i think i created groups by accident 
ill look into creating the end walls as an object with the long walls , thanks fr the help
I’m not sure how you created groups accidentally. I’d be inclined to delete most of the model and start over correctly. And quit nesting the groups.
i was trying to get all objects into 1 group folder and it didnt seem to work ill give it another go from scratch
I’ve fixed your model. It is now reduced to 7 solid components. It should export correctly now.
None of the unneeded complexity.
pitpit solids.skp (1.4 MB)
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how wopuld i create the long walls and ends together ?
I horizontal drew a rectangle at the bottom of the bricks and extruded it downward to give it some thickness. Then I used Push/Pull to pull the edges of the rectangular prism out by 24 mm and used Offset to outline the walls. Then I used Push/Pull to extrude the wall perimeter up to the top of the bricks.
cheers i think i understand , im starting from scratch
Did you look at the copy of the file I made for you?
apologies i didnt see it attached , im going to take myself off to learn how you done those walls , thanks for all your time it means a lot , i use the group as my last resort but really do appreciate the help
