Summer House on concrete base letting in water

Apologies for the bullet points but i thought this might be easier (& quicker to explain)
• our summer house has gone down
• it’s on a concrete base - raised up on wooden base for air flow
• the concrete base touches concrete on both sides so the water has no where to escape
• we are now getting water coming in along both side edges
• we are going to put guttering on the roof on Thursday

My questions are these

• most obviously and importantly, is there anyway to stop this?
• is this all happening because the water has no where to go? I assume it is.
• Should we channel out a gully in the concrete or put some guttering on the concrete as far away from the shed as we can and then fix something to the bottom to draw the water away? I’m thinking of a kind of slope so that any water not going in to the guttering on the roof hits it and slides down in to the guttering and away.

I’ve attached a couple of photos. The one inside looks worse that it is as that’s where we’ve started painting. The water only goes up about 2 inches but as you can see the floor is also wet.

Thanks in advance for any help or suggestions.

Put the shed on concrete slabs raised sufficiently to avoid the flow of water reaching the wooden base of the shed.

Blup

Leaver the structure up a few mm and place wedges in